My contract expires with Arnold Clarke, need advise

almillar

can you advise who is out there as good and as big with the same offers as Arnold Clarke please?

Any main dealer will have PCP deals, as will plenty of big indies. So partially, it depends what car you want. I can't make any personal recommendations though, sorry.

I don't quite get these calculations, can you please explain a bit more?

Yep. You're usually quoted a price, for a number of years, allowing you to drive a certain number of miles per year. That price will be made up of monthly payments (paid every month) and a deposit. In my example, I picked 3 years - 36 months. After you've made these payments in PCP, you have a final payment to make, to own the car. This SHOULD be roughly the value of the car. At the end of your term, you either buy the car for that final payment, and drive away in it, or hand it back, and walk away. Or, as the salesman will try to tell you, 'trade it in' (it's not worth anything) against a new car, and start again.
The bigger the deposit, the smaller the monthly payments, and the less interest you will pay. But the point of my earlier post is to add together all of the monthlies, plus the deposit, then divide back down again, to get a comparable number across different cars and deals.
eg £200 per month, times 35 (the deposit is USUALLY the first payment), plus a £2,000 deposit. That's £9,000. Divide that by 3 - the car will cost £3,000 per year, or divide it by 36, the car will cost £250 per month.