If you are darn sarf they can go in now, oop north it may be worth waiting a week or so. If you can start them with a little bit of shelter, or indoors in pots first it will give the beans chance to gain roots and first growth without the danger of frost. My beans and peas are in and going well in N Wales, but I will be watching the weather this weekend.
I'm in the middle of the country and put mine into pots this week. The pots are in my plastic greenhouse prtecting the beans from the cold nights and to encourage germination. Once the shoots appear I will transfer them to the ground round a wigwam on a warm day in May.
Mine went in 2 weeks ago ( we are on the south coast)... mine are potted up in the polytunnel. if you fancy some early ones just start some now and then do a few more in a couple of weeks and do the same again a couple of weeks later. If you do get caught by the frost at least you will have some spares on the go.