So this pea planting and string cage idea worked out really well! Even the ones which are growing away outside of the string can either be tucked back in or they use their tendrils to cling on. The peas are producing really well and I'm harvesting every few days.
My latest harvest, which joined courgettes, tomatoes, cashews, chillis, spinach and home-grown coriander leaves in a stir-fry with some delicious chilli noodles (The Sharwoods ones that actually have chillis inside the noodles). I admit, some may have just made the pea skins in...as I scoffed the peas out of the fattest ones before I started cooking ;)
Also just realised this placemat is really gorgeous as a background!