By an abolsute twist of fate ive managed to find out wjat frequency this antenna was intended for.
Visiting the scrap yard today for some bits for my 283,000 mile golf, I spied some metal boxes in the corner and remembered that they were the type to which this antenna was attached.
The units were 'aid-call' medical pager units, for people bed-bound on hospital wards.
The main units contain a very large 4x figure-8 led display and a receiver PCB. I purchased all 8 displays and pcbs from the scrappy, upon inspecting the transmitters and receivers I have ascertained that the magic frequency is 173.500mhz :-D
Obviously this is no good for ham use, but I do now have some very high quality FM tx/rx pairs and some large displays to play with.
Still doesn't explain how the antenna works.... oh well.