[binner]

well i have left the top fully open now as im working days so cant get down to uncover on a morning and theye have been baking this week by time i got home. if it stays quite warm il leave it off

[Dave Mack]

Well that throws my theory out of the window, i always advocated planting in June as 100% safe.
Maybe not so then.
Frosts in June, it's supposed to be summer by then. 

It snowed on my birthday 1st June once back in the 1970's 

[Adrian]

If they're already out, you can always cover them with a cloche of some sort, when it gets colder later in the week.

Up here in the north, I wouldn't put anything that is described as "don't put out until all chance of frost has gone" in the ground until after the beginning of June. There again, sometimes you do get tempted to just try one or two courgettes, or whatever. If you have spares in pots, then there's little risk.

Cheers,

Adrian