JAT was experimenting with its livery and this was one of the options.  The roundel on the tail looks misplaced.  LHR looks pretty empty here - there is usually a cluster of jets around the T2 taxiways.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/130275500@N02">G B_NZ</a>
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/130275500@N02/16126681165/">JAT B727-200 YU-AKG at LHR</a>