Sorry, it's understandable that you made a mistake.
And I could name every single one, since I had to memorize all of the the United States presidents in order, including their first names. Then again, I'm American. The only British prime ministers I know are Tony Blair, David Cameron, and William Gladstone.
I have no idea what the first names of the Presidents are, but entering into the world of British Prime Ministers... ready?
Walpole, Wilmington, Pelham, Holles, Cavendish, Stuart, Grenville, Watson-Wentworth, Pitt the Elder, Fitzroy, North, Watson-Wentworth (again), Petty-Fitzmaurice, Bentinck, Pitt the Younger, Addington, Pitt the Younger (again), Grenville (and yes, a relation), Bentinck (again), Perceval, Jenkinson, Canning, Robinson, Wellesley, Grey, Lamb, Wellesley (again), Peel, Melbourne, Peel (again), Russell, Stanley, Hamilton-Gordon, Temple, Stanley (again), Temple (again, Russell (again), Stanley (again), Disraeli, Gladstone, Disraeli (again), Gladstone (again), Gascoyne-Cecil, Gladstone (again), Gascoyne-Cecil (again), Gladstone (again), Primrose, Gascoyne-Cecil (again), Balfour, Campbell-Bannerman, Asquith, George, Law, Baldwin, MacDonald, Baldwin (again), MacDonald (again), Baldwin (again), Chamberlain, Churchill, Attlee, Churchill (again), Eden, MacMillan, Douglas-Home, Wilson, Heath, Wilson (again), Callaghan, Thatcher, Major, Blair, Brown and Cameron.
I can give you a run down of the recent leaders, from Callaghan onwards, but I think that may be a bit much.