Can you rent a car in G.B. when you are over 70. If you have to lease a car what is the shortest leasing period?
There's no national maximum age. I've neve seen a rental agency state one either.
It's been a long time since I've investigated leasing but, for a month or so, renting was always the best deal.
We had been told that you cannot rent a car in Ireland if you're over 70, so when we planned to rent the last time in Great Britain (we typically rent through Hertz) I called them, and they indicated they have no age limit.
When you book a rental car, either online or by phone, you must specify the driver's age, then the rental company will calculate any fee they wish to apply. This is pretty clear when you book through Auto Europe. See also http://www.ricksteves.com/travel-tips/transportation/rental-car-requirements. Leases are usually for three weeks or more and the companies are based in France, so the French car would have to be delivered to the UK for an extra fee. I did that, once, for a long lease, but would not recommend it for a short trip.
Laura's link contains a huge 'may' under age limits and mentions Great Britain (which is an island, not a nation) specifically. Two pieces of imprecision, neither of which matched my knowledge and experience, got me to snooping around.
Autoeurope's site permits rentals from ages 21 to 85 inclusive, but will not allow progression outside this bracket. The point may be moot since AE owns no cars and would be tied to the individual agency's policy.
Hertz's site indicated surcharges under the age of twenty-five but asked for nothing further if you checked the 50+ bracket.
Avis's site indicated surcharges (apparently) for younger drivers, but asked for nothing further if you checked the 25+ bracket.
I checked no others out of boredom.
There are, indeed, leasing agencies in the United Kingdom that will rent for periods ranging from three weeks to something just short of six months - - Peugeot comes immediately to mind. It's doubtful that a car brought over from France would be configured for British driving, regardless of the channel crossing cost.
I far i know there is a problem in you are less than 18 but no problem if you are old. So no need to think about it. You can rent a car and drive.