[ClaireMc]

I've made the classic rookie mistake and planted some squash seeds far too early.  They're outgrowing their little pots on the windowsill and although we have lovely, crumbly well-drained soil, some areas warmed with plastic sheeting, we're in North Yorkshire so there's still a significant frost risk.

Would bigger pots indoors be worthwhile? Or should I chuck them and start again in May?

[corndolly]

I would be tempted to put them into the biggest pots you've got but sow more seed too, just in case.If you have a cold frame you could put them in there and fleece will help with the cold nights.
I'm not an expert on squash but presume they are similar to courgette. Have nt put any seed for these in yet , will start this week.I reckon about 6 wks from seed to planting out and  hope this coincides with last of frost around end of may.

[wellingtons]

... the biggest you can cope with indoors and they'll be fine!

Pop them outside on warm days too ... don't leave them out at night.

[WG.]

I agree with all of the above - especially the suggestion that you re-sow just in case.   Fleece over a cold frame will help but better still try to get a large sheet of bubble wrap.   A good place to get it free is from your friendly neighbourhood furniture store.