My house was built in 1989. Downstairs we have a 1" blue board fix to the internal wall within the cavity. For some reason, I assume cost,they didn't bother to put it upstairs. This is really frustrating because two bedrooms with North facing walls are really cold, and you are not allowed to have blown fiber added if you've already got some insulation (can cause damp).
The best bet for you is to drill a hole into the cavity. If you hit something soft, the you've got insulation. If all you hit is masonary of the second wall, the you've got nothing. Check in a couple of places. If you haven't then get it done - it will make a big difference, especially with the cheap grants around at the moment.
As far as whether you need to have a cavity insulation as part of building regs, i guess it depends on the construction. If thermalite blocks were used, you might not need to have insulation,as the u-value might have met the requirement at that time.