Could someone please tell me what regiment this badge is on the cap?

Rob,

I cant see the picture.

do you have a link?

thats odd-it seems to be working my end. Heres a link:-
http://i43.photobucket.com/albums/e393/afv_rob/SOLDIER.jpg

Well it's pretty hard to make out in the picture unless you can enhance it in any way, but looking through my records, it looks most like the Suffolk Regiment. I'm guessing from the puttees he's not in a cavalry or yeomanry regiment, & the badge looks nothing like any of the supporting Corps. Suffolk would fit in with your region of East Anglia too. The badge would appear to have a scroll underneath & the device in the middle could be a castle.

BTW, if you know or suspect this soldier to be a missing relative from WW1, have you visited the Commonwealth Wargrave Commission site? It has a search engine which allows you to search on surnames, which will give you name, rank, date of death, & location of grave or memorial.