My advice is not to touch it with a barge-pole. Supposing the company goes bust, leaving the pilot with potentially thousands of pounds on "his" credit card. Any reputable company will issue company credit cards, and there are always fuel carnets for the Jet A1. I had to do it a couple of times, but I had confidence in the company I was with at the time. Having said that, my last company re-imbursed me (for a relatively small amount) and then the tax man saw it as an "allowance" and taxed me on it!