Hi lydia it sounds like your seedlings are suffering from something called damping off, basically they are to wet/cold. Do you have a window sill you could put then on? If you can remove the mold with a small artists paint brush from off the top of the compost and let then dry out a little that may help.

Sewing seeds is all about trail and error, if I am using a unheated propagator, as a rule of thumb I start sewing around mothers day, so there's a few weeks for the weather to warm up. I invested in a heated propagator last year so I have started sewing already.

Happy sewing.

I live in the midlands and even with a propagator will not sow until at least the middle to end march depending on the weather, as you have found they come through quickly but then how can you keep them alive and compact until-- here -- the end of may, so I start much later but they seem to catch up ok

Thanks both (sorry for dely in reply!), you're right they were a bit too wet and cold I think. I have dried them out a bit now and they seem to be doing a little better so fingers crossed. Thanks again.