My wife and I are planning a trip to the UK this coming Fall....a few days in London, then up to a time-share in Scotland, then briefly in Ireland. Can any of you UK folks comment on the current cost of petrol in your area? Trying to get a rough idea of how badly we'll get beat up in that regard. Thanks
Iran, who is trying to punish England, France and other EU nations only supplies 3% of their oil. By the time Iran's embargo begins those imports will be closer to zero so there shouldn't be an excessive oil spike like in the US. However it is still around $10 per gallon over there. It will also cost you dearly just to drive and park in London. You might be better off taking trains and buses. And if you aren't used to it, driving on the opposite side of the road is not easy for beginners.
I think Borderlight probably answered your questions with his links.
Best to use tube (subway) and buses in London. Parking and tolls are expensive there. If you're hiring a car go for a diesel if you plan to drive from London to Scotland - will save you a few dollars in fuel.
To expand upon that a bit, right now our plan is to spend some time in London, then fly up to Glasgow where we'll rent a car and drive to a time share not too far from Aviemore for 6 days or so. We'll sightsee about Scotland, then fly from Glasgow to Belfast and spend 5 days traveling about before flying back to London.
You'll pay about £55-£60 for a tank of fuel in a mid sized car (VW Golf ish size) and get between 400-600 miles from that depending on engine type and size. There are a fair few long steepish hills in the Aviemore area so a mid engine size is worthwhile. Can't say for Ireland as I've never been their. Have fun, it's a lovely area of the UK.