Broad beans getting very very tall

I would imagine, with all the rain we've had - that the last thing they would need would be more liquid    Try a granular product if you think the rain has washed all the nutrients from the soil.

the number of beans in the pod is usually the result of poor pollination. There's not much you can do about that as insects can't fly in poor weather 

I would take the tops off. You can either just pinch the tops out, or, if you have plenty of flowers/pods, cut them off further down. This will do two good things. It will remove the very young leaves from the top which are the place that black aphids start colonies. It will also concentrate energy into beans rather than production of new leaves.

Look very carefully for small colonies of black aphids. The first ones will probably be in the young top leaves but you may also find them at the base of young pods. Either rub them off or spray with dilute washing up liquid.

I think they need to donate some of their growth to my broad beans, which are only 8 " high.  I think this is purely down to the cold and wind plus the attention of pea and bean weevil and slugs.

No blackfly but small roundish-oval shaped holes like pinpricks. At first glance they look like blackfly. Something making small holes (and other plants) and it isn't slugs.

100% sure they are small holes as I can see right through them.