Personally, I work on the 2 second rule of safe driving. If someone is tailgating, I'll slow down so there's a 2 second gap between us.
If there's an oppertunity for them to get passed, fair enough, if not they can sit at whatever speed that 2 second gap entails for their and my safety.
Doing so definitely* saved a rear end collision/auld wifie getting flattened in Edinburgh as I had to "slam on" the brakes at about 10 mph when she stepped out in front of me. Gave the previously tailgating c**t behind me that 2 second gap to stop. *(Yes, I know had I being doing 30mph we'd both been past her but still...)