It looks like caterpillar damage to me, but see what others say.

Bean leaf beetle if you have them in the UK. If not, some other sort of beetle. To reduce damage to your beans, next time try planting between other veggies if you can or plant a bit heavier than recommended. The bean leaf beetle has a broader appetite than just beans and other plants can be on its dinner plate too.

No its not caterpillars, I have checked for that and I cannot see any kind of beetles on the plants, that is what is baffling me!

You might try going out at night and have a look underneath the leaves since in many cases these pests are bottom feeders which are those that do their business underneath the leaf and not on the top.