Possibly a Class 127 diesel multiple unit train seen near to Luton.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47739225@N08">citytransportinfo</a>
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/citytransportinfo/38535998265/">DMU Luton area trees</a>