Thanks all for the very useful comments and questions so far. I've got a lot to think about (and a lot to beat myself up about too!).
The last point about re-financing is a good one, that is another option. I could probably get a £25k personal loan at 3% which over 5Y would bump payments up to about £450pm but would save about £100pm in interest in the early months I think but would have less monthly cash to invest.
A lot of number crunching to do... (including ongoing maintenance etc)
As others have said, you need to think about your goals. This website is mostly for people who want to save enough money to retire early. That requires not making the "normal" decisions like spending all your money on a depreciating asset like a car and paying interest on that "asset". Is your goal to have a nice car to enjoy while you work till 65? If so, keep the luxury SUV a year and then buy another every year or two. Tons of people take that path because it's easy and is nice right now. If your goal is financial independence with the option to retire early, you need to look hard at what that car is costing you. It's amazing what vehicles can cost between depreciation, profit for dealers, interest, taxes, registration, maintenance, fuel, etc. LOTS of people spend enough on vehicles to fund a very nice retirement at 60. ($400/month invested at 7% return for 40 years is over $1,000,000.) Setting a goal and really thinking about how nice financial independence would be could help you to decide it's worth it to drive a more sensible car.
If you decide you want to be more intentional about how you spend your money, definitely sell that crazy expensive SUV. You lost money buying it. That money is gone. If you sell it, you aren't really losing more money, you are just admitting you already did. Buy something you like that's much more sensible. Keep if for a long time (transaction costs on vehicles are high).