With regards to Britania at Kemble -XM496, it did indeed taxi under it's own power several times as I was one of those fortunate enough to be part of the crew for doing so. But that was in the late 90's. Not sure if has done anything for the last 10-12 years, as due to work I moved away and hav'nt been involved other than the odd visit.
Brgds
W.G