My toms are starting to get big they are in 3ins pots should I re-pot or just leave them until I plant outside.
I would tollerate a period of pot-bound-ness, but not long - say max 2 weeks.
So my advice would be that when they get pot bound if you will be able to plant out in 2 weeks leave them, if not them pot them on.
My gut feeling is that 3" is way too small to hold the plant until planting out; even if you are in a properly urban heat-island in SE2?? I doubt you could plant out until 01-May? and that's 4 weeks away.
I'm just about to pot on my 9cm / 3.5" potted Tomatoes to 1L / 5" as they are "ready".