Sorry Tigs
Henry Allingham isn't the last.
Wikipedia lists the following still surviving as well as the veterans from other countries.
Allingham, Henry, b. 6 June 1896
Butcher, Stephen, Navy, b. 20 February 1904
Choles, Claude, Navy, b. 3 March 1901 (born in the UK and fought in the British army; subsequently emigrated to Australia)
Cummins, Kenneth, Navy, b. 6 March 1900
Lawton, Professor Harold, East Yorkshire Regiment, b. 27 July 1899
Lucas, Syd(ney), b. 21 September 1900 (Australian resident; fought for the UK)
Newcombe, Harry, Sussex Regiment, b. circa 1900
Pajaczkowski, Jerzy, b. 19 July 1894 (born in Austria-Hungary)
Patch, Harry, Duke of Cornwall's Light Infantry, b. 17 June 1898
Rigby, Andrew, First Lancashire Fusiliers, b. 2 November 1900
Roberts, William ("Bill"), Royal Flying Corps, b. 29 September 1900
Stone, William ("Bill"), Navy, b. 23 September 1900
Swarbrick, Nicholas, Merchant Navy, b. 14 November 1898
Young, Will(iam), Royal Flying Corps, b. 4 January 1900 (same as for Choles and Lucas; went over to Australia after World War II)