hanging baskets

Tbh, not til all risk of frost has passed. You are in a cooler part of the UK, aren't you, so I'd say early June.

Dont know about your but agree with Cn but I never put my hanging baskets out till 2nd week in June when all frosts should be past but this could be wrong this year as so cold yet.

Good question I started Harding plants in my greenhouse about a week 10 days ago if the plants in the basket are hardy they should be OK but do keep an eye on the weather and if they is going to be a frost bring back in overnight I also live in West Yorkshire