Tom, you need to tell people that you are in the UK, it's a lot different when it comes to chicken keeping, especially when it comes to ex-batts.
If you click on Profile, in the blue bar above you can add info about location under your username/avvie.
I have friends in England and Scotland who rescued ex-batts. There were mixed reactions and some problems along the way. The hens were in poor shape and needed extra care. They had no idea about using a nest box, eating pellets, roosting at night or free ranging. Very skittish around people. I seem to recall quite a few had lice and/or mites that required tedious treatment. They were off and on layers, one friend had several go broody and they were not good broody hens, killed the chicks.
I'm not trying to discourage you, only to say go into it with eyes wide open. Quarantine, inspect carefully and they will probably not ever be very friendly. Poor birds started out wrong, so if you are willing to be patient and careful, go for it and best wishes!