You keep mentioning your credit score, but what has gone wrong for you finance wise in the past few years? Credit scores don't mean anything to lenders, they're just random numbers sold to people who don't understand how the system works.
Lenders look at your credit file and previous history of repaying debt. Have you missed payments on credit cards or loans, or have CCJs? Do you use an overdraft, which is seen as bad by lenders?
You have a good income and while not as much spare money as you initially suggested, you seem to have a reasonable handle on your finances.
However, do you have any savings? If you do have £200 spare a month, you should have, because savings would build up over time. Plus if you don't have any savings, you would question whether you can afford to repay a loan and run a car, because maybe you don't have as much spare money as you think?
Do you need a car now? If you have a good relationship with your own bank, they may offer a reasonably priced loan, which could work out cheaper than finance, which is often expensive whether you have a good or bad credit history.