Oil is purchased in US Dollars.
The pound has dropped significantly against the US$
£1 = $1.37 last year
£1 = $1.09 yesterday
So no matter if the price of oil falls, we still are going to have relatively high oil prices which links to petrol and diesel prices.
I don't know how this relates to buying gas - but with our currency falling, it's going to cost us more to buy from other countries.