Bigger injectors
 

are they worth it avec uprated fuel pump? what sort of gains would i see and what cc/size would you go for on a uk turbo?

No gains to be had by replacing injectors alone unless you are near 100%IDC. Even then you would need a map tweak to see any benefits.

they would help with bhp gain with supporting mods though, after a map? yes?

They would, but again, only if the original injectors were struggling as un-ink suggested.