I love virtually all startups and wish for their success. That said: I'm thinking that when every bank in Creation was saying "We won't take CC payments for that. No, no, you simply can't convince us that is a good idea." they were actually being appropriately conservative about legitimate operation risks uniquely incurred by this business model.
If you don't have a Fraud Guy, I respectfully suggest either hiring or training a Fraud Guy very, very soon, preferably before enabling any form of credit card payment. Your Fraud Guy is going to have some recommendations, including recommendations which meaningfully interfere with the product team's ability to meet user demands. If you do not listen to your Fraud Guy's recommendations (or, regrettably, even if you do), you may eventually get an expensive lesson in why both BigCo and startups in related fields eventually have to hire a/several/an entire department of Fraud Guys.
One of your Fraud Guy's first questions is going to be "Is there any pathway by which I can take a credit card and turn it into cash using this service? If so, what is the timeline on that?" I am not a Fraud Guy, but I count two ways to cash out credit cards, just reading the website FAQs. If you are discovered by the adversaries to be the weakest link in the UK financial system with regards to cash outs, you can expect heavy, dedicated adversarial interest.