The Web is a great boon to travellers. Where once you had to sit like a prune on a travel agents chair while they fiddled about for hours on a computer, now you can tailor make your own holiday from your own living room.
As well as the vendor sites, there are these web sites, which purport to search for and sort whatever you are looking for. At the top of the list are what purport to be the best bargains, and the unwary might simply click on these and look no further.
If you type UK car hire into Google, an array of sites like this one appear high on the list. It invites you to enter dates, a pickup location, and a car type, and then runs a search "of up to 40 companies" for you.
A couple of things should be born in mind when interpreting these results. One is that only 4 companies actually have representation at the airport. From memory these are Avis, Budget, Europcar, and Hertz. The others are scattered through West London, take ages to pick you up, and are hellish difficult to find when you need to drop the car off.
Another is that the "search" website quotes a very bare hire price. When I ran a search a couple of weeks ago, Thrifty quoted £322 for 9 days, which is approximately £ 36 a day - and very reasonable it seemed. They told me in advance that 2 child seats would add £5 a day each, bringing the rental to £46 a day - still quite reasonable. What they did not tell me that collision damage waiver, which used to be about £5 a day, was now an extra £18 a day. That, and a few other extras, brought the total price for the nine days to £649, which was more than double the original quote at nearly £76 a day. They also offered to sting me for even more if I wanted automatic transmission.
So while the "search" websites might be a useful first step to identify suitable car models, the wary traveller should then go to the four airport based companies and get detailed quotes including all extras, collision damage waiver, and automatic transmission, if required.