It is viable for people to heat their houses with log fires. However it is inconvenient. You need more tons of logs than tons of coal, and you have to carry the things about instead of turning a tap.
It is viable to run a power station on straw and woodchips. Again it is not as convenient as using piped gas or oil.
However, if you are willing to believe:
(1) fossil fuel is not inexhaustible
(2) fossil fuels damage the planet
(3) the era of cheap energy is not a permanent condition
then it becomes easier to understand that oil is not the only fuel, and that there are alternatives. It also becomes easier to believe that profligate use of energy will not continue indefinitely, even in the countries which today have a cheap energy policy.
edited: And that maybe we will not be running 20 million motor vehicles for ever. The "Present System" may not last for ever. here's to a soft landing!
There is no particular reason to suppose that this country would stop importing sources of energy just because the form those sources took was different. This is a specious argument intended to confuse. The inabiity of the GB land mass to provide enough food, or enough oil and petrol is nothing new.