Well, looking at the forecast down here, things aren't going to improve wet wise for two weeks at least. Tipping down again now, front after front, not so wet in the east obviously. So one might as well plant the potatoes in a bed covered from the rain as best as can be managed. At least they have as much warmth as is possible, and as little wet as possible. Another month of hanging around and it won't be worth planting any main crop potatoes.
The weather has been largely "stuck" for months now, other than the beast, and I don't see any sign of it changing. Worst Autumn/Winter/Spring I can remember by quite some distance. 2013 was a doddle compared to this year.
Logic would say even if some of the first potatoes rotted and didn't appear after 4 weeks, some more could always be planted out at the same time as those that are hanging back anyway. It's only a tenner lost. I would rather "dual run", possibly lose part of the first attempt, than get no potatoes at all. This logic bears in mind blight almost always appears on our site down here in July. A late April maincrop planting is almost pointless. My maincrop went in yesterday under cover.
In the end, even commercial growers' crops fail sometimes. Who can remember the Southern/Spanish crop shortage last year in the supermarkets ?