" wrote in message

I am only following instructions, which say to leave the tomato
plants
in the 3" pots until they flower, and then to plant them out. These
are contrary to my mum's instructions which are to plant them out
"when
they are big enough".

The idea of keeping tomatoes in small pots and treated tough (slightly
pot bound and not watered a lot) is so they "think" they are dying and
thus they begin to flower. (ie fruit fast so that the seeds for the
next generation are created before dying). This usually works well
but they do need to be watched closely. If you can get it right they
power on once planted outside.

I can't comment on whehter they should be outside now as I'm not in
the UK.