Any idea what this is?

From the Stilltime Pictures site that Pogno linked to

http://forum.keypublishing.com/showthread.php?127023-Some-Interesting-Pictures-From-Boscombe-Down-taken-early-1950-s&p=2077230#post2077230

I read the serial as R3435, which would be an Anson, but it looks like a ‘Bitsa’

http://www.stilltimecollection.co.uk/detail/253-celebs1-sir-stafford-cripps-tpt-transport-air-aero-stirling-beaufighter-fire-flame-burn-burning-fighter-crash-rescue.html