There's a list of recommended vets on the Poultrykeeperwebsite, here https://poultrykeeper.com/poultry-vets/#Warwickshire as a starting point, but some if the info may be out of date, you'll need to check.
Ended up taking her to Avondale kenilworth - there's a guy there called by Kieran who is a chicken 'expert'. He was really kind and don't look st me like a nutter when I cried when he told me the bad news. RIP Gert
Sorry about Gert. You did the right thing and its good to know about Avondale and Kieran. I was trying to hold it together when I unfortunately had to take Teabag my hen under very similar circumstances. Obviously didn’t hide my reaction very well (though I knew she was going before I got there) as the staff sent me a card the next day.