You don't mention where you are in the UK but I am waiting to the end of the month,maybe even into June!

I'm in West Yorkshire

I agree it does depend where you live and the temp/frost risks. I am in East Sussex and usually am able to put mine out in April, but this year its been so cold I waited till this week.

Certainly would not recommend for anywhere in northern England or Scotland.

I wouldn't recommend for London and the South East either - the overnight temperature only 6 days ago was 2degC, sufficient for ground frost.
Usual professional recommendation, even in a good year, is to keep summer bedding under cover until the end of May - in a good year, you can risk mid May, specially in the south and west, but in a bad year (like this one) end of May it is. Even then, we're not totally risk free - I recall a frost as late of 4th June about 20 years ago, but that is rare.

To be honest I've never seen the point of summer bedding in our neck of the woods... in a bad year you wait until mid June to plant out and frost can occur at any time.

The weather is not unpredictable - it's boggin' awful! I have been sowing peas and such like in totaly unsuitable conditions because they just will not get sown otherwise.

I usually wait until the spring bank holiday but even then be careful because of the frosts, if you put them out in this cold windy wet weather it could take them ages to recover

Used to be recommended that bedding was done after Derby Day.
Latest ever frost we had here was July 7th. We do not do tender bedding as we can get down to below 5c almost any night of the year. This part of West Midlands/East Wales is a frost pocket with a vengeance.