20-30k miles per annum forces you into a diesel regardless. Your savings will be circa 100/month on fuel.
Man math from my local Costco:
Diesel:
112p/l (premium diesel) @ 50mpg for 20,000 miles = £2,036.65 per year in fuel
Petrol:
109p/l (premium petrol) @30mpg for 20,000 miles = £3,303.49 per year in fuel.
You can fiddle here:
https://www.which.co.uk/reviews/new-...sel-calculator
30k miles per annum is gonna put most dealers off a good PCP, as at 120k miles you'll be handing back a corpse, you may wanna seriously look at large deposit + 6yr HP.