I'm lucky and can get my form signed in work cos I'm a nurse. I seem to remember reading that some pharmacists will do it for nothing - Asda/Tescos I think, but I could be wrong. I know superdrug do it but I'm not sure how much they charge. Your LLC should be able to let you know what choices you have locally x
I went to my asthma nurse and she was fine about it, my GP did the initial form and warned me she could charge, tbh I'd be pretty annoyed to pau, considering how expensive LL is anyway.