Great Western Railway high speed train 43128 is bringing up the rear of a diverted south Wales service which is leaving London Marylebone station (rather than the usual terminus at nearby Paddington). When it is clear Chiltern Railway's 168321 will follow it with a normal service on the line.
<a href="//commons.wikimedia.org/wiki/User:Geof_Sheppard" title="User:Geof Sheppard">Geof Sheppard</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>