I had a problem hiring a car in the UK once I had reached my three score and ten. My wife and I usually travel to the UK at least twice a year and mainly via air.
At the end of 2012 I had difficulty trying to find a car out of Gatwick. I mentioned this on one of our Forums and a helpful member suggested that I try Indigo Car Hire.The following year (Oct.) I contacted Indigo who organised me a car through Budget. This trip was via Stansted and I had a week's hire of a "Stop-Start" FIAT 500 for well under £100.
Up until I found Indigo, I had discovered that it was difficult to find a car hire company that would take hirers over 70. Not only did this hire company arrange the car hire but it also organised the excess insurance which was about a third of what Budget (Avis) would have asked.
I can recommend this company highly - it was one of the most helpful I have ever come across in more than 50 years of hiring cars. It's worth having a look at Indigo's forum:
http://indigocarhire.co.uk/forums/viewtopic.php?f=24&t=25
I am just about to book our car hire for this year's Christmas trip to the UK.