How does one address the members of the nobility or the aristocracy in England. That depends on whether a person is speaking directly to the person, writing to the person informally, and writing to the person in a formal situation.

Royalty
For each entry, one will find the following pattern:

Position
On envelopes
Salutation in letter
Oral address

King
His Majesty The King
Your Majesty
Your Majesty, and thereafter as “Sir/Sire”

Queen
Her Majesty The Queen
Your Majesty
Your Majesty, and thereafter as “Ma’am”

Prince of Wales
His Royal Highness The Prince of Wales
Your Royal Highness
Your Royal Highness, and thereafter as “Sir”

Wife of the Prince of Wales
Her Royal Highness The Princess of Wales (traditionally)
(or) Her Royal Highness The Duchess of Cornwall
(or) Her Royal Highness The Duchess of Rothesay (an exception to tradition since 2005)
Your Royal Highness
Your Royal Highness, and thereafter as “Ma’am”

Princess Royal
HRH The Princess Royal
Your Royal Highness
Your Royal Highness, and thereafter as “Ma’am”

Royal Peer
HRH The Duke of XXX, e.g., HRH The Duke of Cambridge
Your Royal Highness
Your Royal Highness, and thereafter as “Sir”

Royal Peeress
HRH The Duchess of XXX, e.g., HRH The Duchess of Cambridge
Your Royal Highness
Your Royal Highness, and thereafter as “Ma’am”

Sovereign’s Son
(unless a peer) HRH The Prince XXX, e.g. HRH The Prince John
Your Royal Highness
Your Royal Highness, and thereafter as “Sir”

Sovereign’s son’s wife
(unless a peeress) HRH The Princess XXX, e.g. HRH The Princess John
Your Royal Highness
Your Royal Highness, and thereafter as “Ma’am”

Sovereign’s Daughter
(unless a peeress)
HRH The Princess XXX
Your Royal Highness
Your Royal Highness, and thereafter as “Ma’am”

Sons of the Prince of Wales
(unless a peer) HRH Prince XXX of Wales, e.g., HRH Prince Frederick of Wales
Your Royal Highness
Your Royal Highness, and thereafter as “Sir”

Sovereign’s son’s son, Prince of Wales’s eldest son’s sons
(unless a peer) HRH Prince XXX of XXX, e.g. HRH Prince Michael of Kent
Your Royal Highness
Your Royal Highness, and thereafter as “Sir”

Sovereign’s son’s son’s wife
(unless a peeress) HRH Princess XXX of XXX, e.g., HRH Princess Michael of Kent
Your Royal Highness
Your Royal Highness, and thereafter as “Ma’am”

Sovereign’s son’s daughter, Prince of Wales’s eldest son’s daughters
(unless a peeress) HRH Princess XXX of XXX, e.g., HRH Princess Beatrice of York
Your Royal Highness
Your Royal Highness

Sovereign’s son’s son’s son
(unless a peer) (Except son of the eldest son of the Prince of Wales) The Lord XXX Windsor, e.g., The Lord Nicholas Windsor
Dear Lord XXX
Lord XXX

Sovereign’s son’s son’s son’s wife
(unless a peeress) The Lady XXX Windsor, e.g., The Lady Nicholas Windsor
Dear Lady XXX
Lady XXX

Sovereign’s son’s son’s daughter
(unless a peeress) The Lady XXX Windsor, e.g., The Lady Helen Taylor
Dear Lady XXX
Lady XXX

A formal announcement in The London Gazette reads: “The Queen has been pleased by Letters Patent under the Great Seal of the Realm dated 31 December 2012 to declare that all the children of the eldest son of the Prince of Wales should have and enjoy the style, title and attribute of Royal Highness with the titular dignity of Prince or Princess prefixed to their Christian names or with such other titles of honour.” This refers to any children of Duke and Duchess of Cambridge.

Nobility
Peers and Peeresses
Position
On Envelopes
Salutation in Letter
Oral Address

Duke
(His Grace) The Duke of XXX
My Lord Duke or Dear Duke (of XXX)
Your Grace or Duke

Duchess
(Her Grace) The Duchess of XXX
Madam or Dear Duchess (of XXX)
Your Grace or Duchess

Marquess or Marquis
(The Most Honourable) The Marquess of XXX
My Lord Marquess or Dear Lord XXX
My Lord or Your Lordship or Lord XXX

Marchioness
(The Most Honourable) The Marchioness of XXX
Madam or Dear Lady XXX
My Lady or Your Ladyship or Lady XXX

Earl
(The Right Honourable) The Earl of XXX
My Lord or Dear Lord XXX
My Lord or Your Lordship or Lord XXX

Countess
(The Rt Hon) The Countess of XXX
Madam or Dear Lady XXX
My Lady or Your Ladyship or Lady XXX

Viscount
(The Rt Hon) The Viscount XXX
My Lord or Dear Lord XXX
My Lord or Your Lordship or Lord XXX

Viscountess
(The Rt Hon) The Viscountess XXX
Madam or Dear Lady XXX
My Lady or Your Ladyship or Lady XXX

Baron (or) Lord of Parliament
(The Rt Hon) The Lord XXX
My Lord or Dear Lord XXX
My Lord or Your Lordship or Lord XXX

Baroness (in her own right)
(The Rt Hon) The Lady XXX or (The Rt Hon) The Baroness XXX
Madam or Dear Lady XXX or Dear Baroness XXX
My Lady or Your Ladyship or Lady XXX or Baroness XXX

Baroness (in her husband’s right) (or) Lady of Parliament (in her or her husband’s right) (The Rt Hon) The Lady XXX
Madam or Dear Lady XXX
My Lady or Your Ladyship or Lady XXX

Eldest sons, grandsons and great-grandsons of dukes, marquesses and earls
Position
On envelopes
alutation in letter
Oral address
Eldest sons of dukes, marquesses and earls use their father’s most senior subsidiary title as courtesy titles: note the absence of “The” before the title. If applicable, eldest sons of courtesy marquesses or courtesy earls also use a subsidiary title from their (great) grandfather, which is lower ranking than the one used by their father. Eldest daughters do not have courtesy titles; all courtesy peeresses are wives of courtesy peers.

Courtesy Marquess
(The) Marquess of XXX
My Lord or Dear Lord XXX
My Lord or Lord XXX

Courtesy Marquess’s Wife
(The) Marchioness of XXX
Madam or Dear Lady XXX
My Lady or Lady XXX

Courtesy Earl
(The) Earl of XXX
My Lord or Dear Lord XXX
My Lord or Lord XXX

Courtesy Earl’s Wife
(The) Countess of XXX
Madam or Dear Lady XXX
My Lady or Lady XXX

Courtesy Viscount
(The) Viscount XXX
My Lord or Dear Lord XXX
My Lord or Lord XXX

Courtesy Viscount’s Wife
(The) Viscountess XXX
Madam or Dear Lady XXX
My Lady or Lady XXX

Courtesy Baron (or) Courtesy Lord of Parliament
(The) Lord XXX
My Lord or Dear Lord XXX
My Lord or Lord XXX

Courtesy Baron’s wife (or) Wife of Courtesy Lord of Parliament
(The) Lady XXX
Madam or Dear Lady XXX
My Lady or Lady XXX

Heirs-apparent and heirs-presumptive of Scottish peers
Position
On envelopes
Salutation in letter
Oral address
Heirs-apparent and heirs-presumptive of Scottish peers use the titles “Master” and “Mistress”; these are substantive, not courtesy titles. If, however, the individual is the eldest son of a Duke, Marquess or Earl, then he uses the appropriate courtesy title, as noted above.

Scottish peer’s heir-apparent or heir-presumptive
The Master of XXX
Sir or
Dear Master of XXX
Sir or Master

Scottish peer’s heiress-apparent or heiress-presumptive
The Mistress of XXX
Madam or Dear Mistress of XXX
Madam or Mistress

Sons, grandsons and great-grandsons of peers
Position
On envelopes
Salutation in letter
Oral address

Duke’s younger son (or) (Courtesy) Marquess’s younger son
(The) Lord XXX XXX, e.g. (The) Lord James Marshall
My Lord or Dear Lord XXX (XXX), e.g. Dear Lord James (Marshall)
My Lord or Lord XXX, e.g. Lord James

Duke’s younger son’s wife (or) (Courtesy) Marquess’s younger son’s wife
(The) Lady XXX XXX, e.g., (The) Lady James Marshall
Madam or Dear Lady XXX, e.g., Dear Lady James
My Lady or Lady XXX, e.g., Lady James

(Courtesy) Earl’s younger son (or) (Courtesy) Viscount’s son (or) (Courtesy) Baron’s son (or) (Courtesy) Lord of Parliament’s son
The Hon XXX XXX, e.g. The Hon James Marshall
Sir or Dear Mr XXX, e.g. Dear Mr Marshall
Sir or Mr XXX, e.g. Mr Marshall

(Courtesy) Earl’s younger son’s wife (or) (Courtesy) Viscount’s son’s wife (or) (Courtesy) Baron’s son’s wife (or) (Courtesy) Lord of Parliament’s son’s wife
The Hon Mrs XXX XXX, e.g. The Hon Mrs James Marshall
Madam or Dear Mrs XXX, e.g. Dear Mrs Marshall
Madam or Mrs XXX, e.g. Mrs Marshall

Daughters, granddaughters and great-granddaughters of peers
Position
On envelopes
Salutation in letter
Oral address
If a daughter of a peer or courtesy peer marries another peer or courtesy peer, she takes her husband’s rank. If she marries anyone else, she keeps her rank and title, using her husband’s surname instead of her maiden name.

Duke’s daughter (or) (Courtesy) Marquess’s daughter (or) (Courtesy) Earl’s daughter (or) (unmarried or married to a commoner)
(The) Lady XXX XXX (if unmarried), e.g. (The) Lady Sarah Brady (or) (The) Lady XXX XXX (Husband Surname, if Married), e.g. (The) Lady Sarah Williams
Madam or Dear Lady XXX, e.g. Dear Lady Sarah
My Lady or Lady XXX, e.g. Lady Sarah

(Courtesy) Viscount’s daughter (or) (Courtesy) Baron’s daughter (or) (Courtesy) Lord of parliament’s daughter (unmarried)
The Hon XXX XXX, e.g. The Hon Melinda Alexander
Madam or Dear Miss XXX, e.g. Dear Miss Alexander
Madam or Miss XXX, e.g. Miss Alexander

(Courtesy) Viscount’s daughter (or) (Courtesy) Baron’s daughter (or) (Courtesy) Lord of Parliament’s daughter(married to a commoner)
The Hon Mrs Brown (Husband Surname)
Madam or Dear Mrs Brown
Madam or Mrs Brown

Gentry and Minor Nobility
Position
On Envelopes
Salutation in Letter
Oral Address

Baronets
Baronet
Sir XXX XXX, Bt (or Bart), e.g. Sir Samuel Smith
Sir or Dear Sir XXX (XXX), e.g. Dear Sir Samuel (Smith)
Sir or Sir XXX, e.g. Sir Samuel

Baronetess in her own right
Dame XXX XXX, Btss, e.g. Dame Samantha Brown, Btss
Madam or Dear Dame XXX (XXX), e.g. Dear Dame Samantha (Brown)
Madam or Dame XXX, e.g. Dame Samantha

Baronet’s wife
Lady XXX, e.g. Lady Lowery
Madam or Dear Lady XXX, e.g. Dear Lady Lowery
My Lady or Lady XXX, e.g. Lady Lowery

Baronet’s divorced wife
XXX, Lady XXX, e.g. Grace, Lady Lowery
Madam or Dear Lady XXX, e.g. Dear Lady Lowery
My Lady or Lady XXX, e.g. Lady Lowery

Baronet’s Widow
Dowager Lady XXX or Lady XXX if the heir incumbent is unmarried, e.g. Dowager Lady Lowery (or) Lady Lowery
Madam or Dear Lady XXX, e.g. Dear Lady Lowery
My Lady or Lady XXX, e.g. Lady Lowery

Knights
Position
On envelopes
Salutation in letter
Oral address

Knight (of any order)
Sir XXX XXX, e.g. Sir James Lucas
Sir or Dear Sir XXX (XXX), e.g. Dear Sir James (Lucas)
Sir or Sir XXX, e.g. Sir James

Lady (of the Order of the Garter or the Thistle)
Lady XXX XXX, e.g. Lady Mary Smith
Madam or Dear Lady XXX (XXX), e.g Dear Lady Mary (Smith)
My Lady or Lady XXX, e.g. Lady Mary

Dame (of an order other than the Garter or the Thistle)
Dame XXX XXX, e.g. Dame Margaret Lowery
Madam or Dear Dame XXX (XXX), Dear Dame Margaret (Lowery)
Madam or Dame XXX, e.g. Dame Margaret

Knight’s Wife
Lady XXX, e.g. Lady Lowery
Madam or Dear XXX XXX, e.g. Dear Lady Lowery
My Lady or Lady XXX, e.g. Lady Lowery