Looks like sun and wind damage

Looks like the work of a cut worm as well as cold damage. Cut worms live in the soil and come up at night to feed on tender pants. You can deter them by making plant collars out of milk container, cups, cans. Just cut open both ends and place over plant. Press collar down into soil about an inch. This will protect the young plant from cut worms.

Frost.

It hasn't gone below 9 degrees here on south coast according to my iPhone weather app! Plus Iv got the fleece wrapped round the outside. I'll try the plastic bottle / milk cup protection! Never heard of cut worms tho I must admit! Maybe put some barrier round to protect from wind, not sure what I can do to protect from sun damage? Never had this problem when I grew them against a wall in pots in my old house so that probably explains the difference in exposure to elements and pests?

I know you don't want to hear this, but it's still early in the season and you should start new runner bean plants. Plant them out with the collar right from the "get go." Also, they're less likely to suffer cold damage. Here is a little video on cutworms and how to make collars to protect young seedlings.

https://www.youtube.com/watch?v=JsXFbmpa0Zc

Agree with Bathgate runner beans can be sown into early June and, in my view, best done direct into the soil where they will grown. You need bamboo canes for the beans to grow up not thick pieces of hazel they are going to find it difficult to twine around.

We have similar or the same in the UK

Leatherjackets are the soil-dwelling larvae of flies known as crane flies , and they eat roots and stem bases.

I agree re sow where you want them to grow

Your right I didn't want to hear any of this haha

It was all the beans I saved from last year! Will have to go buy some now!!

We've all been there, join the party!! Luckily the new seeds will spring up in about 5 days, you'll be the wiser.