There is a Comet 4 at Bruntingthorpe but whether that is live and can taxi I dont know.
That Comet is "Canopus". The last of the airworthy comets and yes, last I heard (or at least read about) she can and often does taxi, including regular high speed runs. There are also a
dedicated band of men and women desperately trying to have her ready to fly in 2008 at the the fiftieth anniversary of regular transatlantic jet flight. Apparently, the only real hurdle to her receiving an airworthyness certificate is the refusal of BAE Systems to release the remaining design drawings.
This may have changed however recently and I'd certainly be interested to hear any more recent news from Bruntingthorpe.