I know it’s old but, this is drivel
Don’t bother with the NHS for this; they are completely, absolutely useless and couldn’t care less about your quality of life.
Some GPs might not refer you well, some physios might not help you well, but NHS physio is why I can ride a bike.
That said, this does sound like a job for a private physio- just for speed as much as anything else. IMO backs are useful things and you only get one so yeah maybe you could amateur stretch it out, or do pilates or something, but it’d be a very good idea to get it properly checked out first to make sure you’re doing hte right thing.