VAT only payable on new vehicles. It's not added to MOT, but is added to repairs if the repair shop has a high enough turnover. Best to find a small place or a guy working on his own.
VAT (value added tax) replaced "purchase tax" many years ago. It started at 7.5%, now it's 20% ! It's charged on almost everything, including services but not food. There are a few exceptions but mostly we all get stung on pretty much everything we buy new. A business registered for VAT can claim back the VAT they've paid on goods and services pertaining to the business, but they must charge VAT on their own goods/services.
It's a great government racket. Spend £100 and £20 goes to the government. Don't get me started on fuel tax and the rest of it. And they wonder why there's a thriving "black economy" (cash only - hush hush)