We don't really have the mental category of "Great British Novel" in the way that people consciously have in the US of "Great American Novel." But anyway:
Early:
Tom Jones by Henry Fielding - comedy, one of the earliest novels in English but very readable.
Tristram Shandy - Laurence Sterne
Victorian:
Trollope (Anthony, not Joanna!). The Warden?
Ivanhoe by Walter Scott
Cranford, North and South - Mrs Gaskell
Wilkie Collins - the Moonstone, the Woman in White
Dracula - Bram Stoker
Prewar:
I second Arnold Bennett - try Anna of the Five Towns.
Dorothy L Sayers' Lord Peter Wimsey mysteries. Very English.
Agatha Christie is very under rated imo.
I Capture the Castle by Dodie Smith (some might argue this is a children's book but I read it as an adult)
Three Men in a Boat - Jerome K Jerome
DH Lawrence?
Post war:
The Quiet American, The Power and the Glory - Graham Greene
Possession, AS Byatt
Lucky Jim - Kingsley Amis
Tinker Tailor Soldier Spy, Le Carre
The Lucia novels by EF Benson
Cider with Rosie - Laurie Lee
The Prime of Miss Jean Brodie - Muriel Spark
Children's books:
Grimble by Clement Freud
The Railway Children, Five Children and It, both Edith Nesbit
Rudyard Kipling - Jungle Book
The Secret Garden, A Little Princess - Frances Hodgson Burnett
The Eagle of the Ninth - Rosemary Sutcliffe
Watership Down - Richard Adams