(I'll answer as if I don't think this is a wind up question. Though I am not sure. )
If you went to the clinic yourself regularly, you would know that the NHS does not give you a certificate. They tell you or text you the result. To get a certificate, one would need to go private. Not likely an escort will do this.
But if one did, since you don't know what a private certificate looks like, there is no way to know if it is a forgery or not, right? And the name on the certificate would need to match the passport. So you need to see her real name and passport too. Not at all going to happen.
And then, she asks you to share your certificate. And you give her what?
You are a nervous punter, but you start at Phoenix club. Really?
If this is not a wind up question, always use your best judgement. Avoid barebackers. And hold your nerve. Or take up golf.