Today I found my one surviving colony almost dead from isolation starvation. On May 15th!
They had clustered on the brood, as might be expected; bees very rarely abandon it. But they were a couple of inches from the food, and it must have been too cold for them to be able to bridge the gap. I spotted that no bees were flying on a mild afternoon, opened it up, and they were obviously very weak. When I pulled some frames, I found bees that were obviously dying. The queen was still alive though, so I doused them with sugar syrup. That started to wake them up, and by the time I came home, a few were beginning to fly. The weather's getting warmer, so they should be OK now. It will have set them right back though, and I'm not expecting any honey this year.
I've planted out more peas; Latvian Pea, Irish Preans, Lancashire Lad, Victorian Purple Podded, Commander, and Clarke's Beltony Blue, and started a few more in pots. The beans are looking a bit sorry for themselves, but they're OK. Some of the sweet corn was finished off by the frost, but 35 out of the original 60 I planted are alive, with more to come. Not all the seeds germinated, but I'm not complaining. It'll give me some nice early corn, and spread the season a bit.