I'm no plant expert and I don't know UK plants, so verify what I say here with someone more knowledgable than me, but the first on looks like sow thistle and the second one looks like regular thistle to me. I feed both of those to my tortoises.
Pull up Tortoise Table and study all the plants there, keep cross referencing with what you see around. Don't ever pick up any weeds from public spaces where the grounds are being maintained by city crews. They maybe using chemicals, plus people walk their dogs some of whom maybe on heartworm meds which are then excreted and if ingested by torts can be lethal for them. Check out your supermarket, many sell dandelion greens, get endive, escarole, frisée lettuces and collard greens. Get some Mazuri, soak few pellets and see if he likes them. If so, try finely chopping your mixed greens and mix that with Mazuri mash. Just keep trying different things. I like chopping things very finely for babies and sick torts. Mushy food is much easier to eat and takes less energy to put in their mouth, no biting, no tearing saves a lot of breath power for chewing and swallowing so whenever tort is recovering from illness especially respiratory one, making food easy for them to eat is essential