IGotOut,
I was educated in the 80s - and we did our science in metric. Which I'm perfectly comfortable with. I can't now remember if what little cookery we did was done in metric or imperial - but in that case the greatest influence on me was Mum. She cooked in imperial and that's still how I think when planning a meal - if following a recipe it'll be metric - but when buying meat or fruit and veg I still estinmate in imperial and convert if forced to buy that way. It's not like converting 3/41b into kg is hard.
If I'm doing DIY, then the influence on me was Dad. Again, of an older school who thought in imperial. So that's how I mostly estimate distances, and the foot and inch are more convenient for imprecise measurements that mm, cm or m anyway. If I'm working out how much paint I need, or measuring precisely, then I'll use metric.
For work it's metric all the way. I measure water in litres, because 1,000L is a convenient 1m³ of water that conveniently also gives you a nice 1000kg. Pressure should be in bar, because the numbers are smaller, and litres per second is easier than gallons per minute.
I saw a survey in the Eurozone a couple of years ago that said that more than half of people still translate how much stuff costs into their original currencies to work out how much it should be, despite the Euro having been with us for two decades! I know I did it when I lived in Belgium, but then I had the disadvantage that I was only just getting used to the Belgian franc when they unsportingly turned them all into Euros while I was in Blightly visiting my family over Christmas/New Year.
It's not so much stubborness, as people being slow to change the ways they think. Especially when you're doing that kind of sense-checking estimation in your head that tells you if a proper calculation is actually in the right ball-park. Neither is it a uniquely British thing. It's simply people being people.