UPDATE - 6 July 2019: Since I first posted the "NOT working" notice below, I have received exactly one email requesting re-creation of my hire base maps. So unless there are a sudden flurry of requests, it looks as though they will be permanently laid to rest.
14 Jan 2019: The map is NOT working, and apparently has not been working for quite a long time. I did not notice, because I had no reason to check it, naively believing that it would just continue to work. However, at some point, Google changed the map interface and disallowed the old version. They never told me, before pulling the rug out from under, though they could have since all map requests from this site are identified by a unique key. Unfortunately, the changes required to get a working map appear to be extensive, and a complete rewrite of the code on this page is probably needed.
So, my apologies. I will leave the defunct map lying here for now. However, I you think it would be useful to you, please email me at the address at the bottom of this page. If I get enough interest, I will try to recreate the map. (If I do recreate it though, I will probably switch to some open-source project instead of depending on a large firm like Google.)
Click marker on map to identify base. Or click firm/base name on right to highlight its location.
You can, of course, zoom and pan the map as you wish. Panning is most easily done by simply moving your cursor onto the map, holding down the left mouse button (on PCs), and "dragging" the map.
Clicking on the firm/base name on the right will also give you access to links which will display a zoomed-in aerial view for the base's location, either on bing.com (was live.com) or google maps. bing.com often provides a higher resolution view than google maps (though frequently older). Note that the bing.com view, which comes from Microsoft, may only work on Macs if you use the Firefox web browser.
Note that on the google zoomed-in view one *may* have access to a street-level view, if available at that location. Bing.com on the other hand, will usually give access to a "birds-eye" view (from a low-flying aircraft rather than a satellite).
NOTE: I recently noticed that the google zoomed-in maps had stopped working properly, apparently due to a change by google in which they carelessly broke existing maps. I have made some changes and the maps should work correctly now.
Asterisks on base names on the right indicate status - no asterisk means the location is accurate. Please report any inaccurate locations that you discover.
Also available: Map of Hire Bases in England and Wales
Many thanks to Graham Keens for finding the locations of the bases for the large multiple-base firms.