Light is your main problem - even in a south facing window, the one-
sided light is nowhere near as good as the long days of overhead light
in the summer. At one time you could get radishes which were bred to be
grown in a greenhouse over the winter.

I'd suggest - in the spring, use the window sill to get crops started a
wee bit earlier (but not too early as they'll go leggy with the lack of
light), then in autumn use it to extend the ripening period for things
which you have started outside in pots.

Thanks, both - I didn't realise they would be so useless. I had lettuces
going in them over the summer, which went bananas (but did lean towards the
window, so I had to turn the box round every so often).

I dream of spring . . . (wishing my life away!)

Andrew
http://greencottage.burysolarclub.net