Not sure about accurate Stone Age (i.e. Non "caveman") types. Remember the Stone Age itself is a vast period of time. If you google "doggerland" you'll get some Mesolithic people. Britain really didn't have much of a population until the Neolithic period but chucking those terms in and sifting the results carefully might help.
For copper and early bromze age you could start with a look at the Beaker people, Otzi "the iceman" is copper age and although from Italy googling him will give you lots of background and ideas. Closer to home the "Amesbury Archer" is worth a look, although he was probably not British in origin.
Later bronze and iron age Britons can be drawn from celtic figure ranges although tribe to tribe may have varied greatly (Celt is more a cultural term than a specific people) and the people of the north of Britain may have looked quite different from those of the south, east or west.
The Roman period is a long time and had both romanised Brits who looked like Romans, traditional Brits and again those from the North and Ireland who were much less influenced by the empire. So you can use Celts and later early dark age/ Arthurian figures for the 400 or so years of the occupation up til the coming of the Germans in the 5th century.
Not sure if that's a lot of help, I'm generalising a great deal, but it should point in the right direction.