We need to use UK oil and gas ,not buy it in 
it's not green to import when we are still burning oil and gas
we may as well use our own .
But it's not 'our own'. It's Shell's, or BP's or ExonMobile's, or whoever extract's it from the ground/sea bed. Once extracted, those companies sell it on the world market at whatever the prevailing world market price is. If you attempted to tell them they could only sell it to the UK market, at below world prices, they'd tell you to eff-orf. And anyway, there isn't enough oil/gas in the North sea to materially affect world oil prices.
The only way the UK could insulate itself from this would be to setup (or nationalise) a state oil/gas company, which being government controlled would 'sell' to the UK market at price below the market rate. That's proper communist thinking that I doubt even a Corbyn lead Labour party could support.
That being the case, why then do consumers in the USA pay much lower prices than we do ?
Two basic reasons - economy of scale, and taxes.
According to wiki (
https://en.wikipedia.org/wiki/File:Gasoline_Diesel_Taxes.webp) US Federal tax is 18.4 c/gal, and state taxes can bump this up to anything up to 86c/gal. The state most people visit (California) its a total of 85c/gal, and some states also have an additional sales tax. If crossing from Nevada(50c/gal) or Arizona(19c/gal) into CA you soon learn to fill up before crossing the border.
Fuel prices in California are approaching $6 a gallon, so the 'tax' content (86c/gal) is roughly 15%. Therefore the pre-tax cost of a gallon of fuel is $5.14 ish
In the UK, fuel duty is 57.95p/gal, and 'sales tax' (VAT) is 20% on top. Total pump price here is about £6.20/US gallon. Of that 57.95p is duty, and £1.03 is VAT, so the underlying pre-tax cost is £4.59 per US gallon. With an exchange rate of roughly 1.32, £4.59 is roughly $6.07.
Given that we in the UK seem to pay a 1:1 exchange rate for most US$ priced stuff, I'm actually quite surprised we pay as little as we do for petrol.
The US does have what they call a strategic oil reserve, and the federal govt can release this onto the domestic market to try and smooth out tempoary fuel price spikes (they call it price gouging). The UK govt doesn't have any significant reserves.