Sudden and rapid demise of tomato seedlings

Digger, planting toms now for moving on to the greenhouse is fine - if you've got one. Same with enough windows, let alone sunny ones. Yummy might not have the amount of windows you do and it doesn't sound as if there's a greenhouse either. I suspect some folks are working with 1, possibly 2, windows to start things. So, please don't discount some things so quickly  

Cheers everyone for the advice.

I only planted them because it said it was ok on the packet. I'm a novice and didn't know any different really. But then I guess you learn from your mistakes. Won't do it so early next year.

Yeah I only have a couple of windows where the seeds will be safe from the dogs noses/gobs   and we don't have a greenhouse yet either. I did start on windowsil last time but they went really leggy. Mind you I didn't know about the ally foil trick back then until someone on here told me about it.

I still have 10 plants that look to be growing strong at the moment and hopefully they will stay that way. If not then I have a packet of gardeners delight and I will try again with those in a couple of weeks.