U.K. petrol is pricey
Prepare for REALLY expensive gas
That petrol (gasoline) may look reasonably priced, but remember the posted price is per liter, not per gallon—and it's in pounds, not dollars.
As of mid-2017, the average U.K. price for petrol was £1.19 per litre, which works out to $5.74 per gallon.
For an American to get an accurate sense of how much gas costs, you have to multiply the per-liter price by 3.8 to get gallons (doing it in your head, just use 4), then multiply that by the current exchange rate (estimate about $1.35 to £1) to get it into dollars.
Then have someone with a defibrillator handy get your heart started again.