re: zebedies remark on the Australia trials with transponders - Good point, but I believe (and am happy to be proved wrong
) that these were Mode A/C only transponders and as a result gaggles of gliders in one area caused lots of garbling and hassle for ATC to negate any benefit.
As any new fit transponder must be Mode S in the UK, and all non-Mode S SSR radars will not get approval to operate from 2012 (unless credible replacement plan in place) in UK, in the future there should be no reason why a group of gliders could not be tracked quite happily by any unit with a Mode S radar.
In saying tracked I mean from a system level, having a whole bunch of overlapping lables presented to a controller is a different issue, and one I don't have to deal with
Of course, ADS-B could be the way forward. You don't need a fully capable Mode S transponder to broadcast ADS-B squitters.