I have found a packet of 'dwarf beans' (Mr Fothergills).
Are these the same as French beans? It states to plant out from April to July on the packet.
Probably. There are dwarf runner beans though. Plant some in a pot in April and see what comes up? What's the worst that can happen? You get beans you don't like? True, this strategy had a few drawbacks for Jack but I'm pretty sure those beans weren't dwarf ones
I think they would be French Beans, usually Runner Bean seed is much bigger than French Bean, Dwarf or Climbing! Think of the relative size of the pod they come from, Runner Bean seed is about the size of the first joint of the Thumb whereas French Bean is about the size of the first joint of your little finger. You should find some pictures in seed catalogues or on line. On another point check the sow by date on the pack French Bean seed does not keep nearly as long as Runner Bean.