As Andrew Gray suggests (Letters, 17 December) shale was once the only source of petroleum oil produced in the UK. Before that, other fats and oils – some from whales and other marine sources – were used for lighting.
My letter (15 December) referred to a period when there was a considerable shale oil industry in Scotland which, among other things, produced petrol for motor vehicles.
By that time petroleum was being imported from elsewhere, mainly the Middle East, and refined here to produce petrol.
Petrol from shale could compete when taxed at the same rate as that from imported oil, but not when taxed at a higher rate.
I therefore repeat my statement that tax imposed by a UK government killed the Scottish shale oil industry.
How long that industry would have survived if the differential tax had not been imposed I do not know.
Remaining reserves of shale are an asset for our future if and when we need them.