Presumably in BHX to undertake some radar calibration.  A HS-125 sits behind the 748.
<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@N02/23464505254/">CAA HS748 G-AVXJ in BHX</a>