There are still large untapped known fields in the North Sea within UK waters adjacent to the same that Norway are still profitably using. There is also vast swathes of UK waters that are unexplored, and are currently artificially expensive to do so due to UK taxation on fossil fuel companies.

The price of petrol at the pump is at least 50% Government direct tax - fuel duty, VAT (which multiplies the duty value - very cheeky). Then the other parts - wholesale price, retailer profit, delivery costs, have their tax implicitly priced into that. That probably makes the overall Government take something like 70% of the price you pay.

As for coal, there's apparently about 600 million tons of accessible usable coal left, which at current UK usage is good for quite a few decades if not more.