Why does England still use miles although everything else is on the metric system?

Historically the road network in England was established by the Romans who measured in miles. The metric system was first introduced to France by Napoleon at a time when they were at war with England. This is why the English were reluctant to adopt metrification. Since joining the European Union in 1973, the UK has had to use metric measures for some products to comply with the rest of the continent. But the metric system doesn't apply to everything; beer and milk are still sold in pints and a person's weight is measured in stones. I believe the main reason that England still uses miles is because the British government doesn't want to spend money updating their road signs and maps. Same reason they still drive on the left. It's easy and cheap for parliament to pass legislation compelling manufacturers and merchants to make and sell goods in kilograms and litres, but the government won't invest in converting their ouwn departments to metric.