Viewed here from nearby footbridge was Tarmac Trackwork road/rail Unimog with running number 538010 working on Jubilee line extension.
Also seen here at various times were other tarmac owned plant items with running numbers 538001/538002/530007/538009.
Any help with these much appreciated
538009 is now Stobart W020. If you search for Tarmac two other unimogs pop up but not by 538xxx number.
538002 is the tamper now at Welsh Highland Railway.
The Unimog with the number 538010 was a U1650 Pick up Shunter with Registration number Q719VOH (but carried Q179VOH in error). Builders number WDB4271151W166200 and was Channel Tunnel No. 81 (Tarmac Construction) and was ex Jones Plant Services, ex Centrac 538010. Hope this helps.
Many thanks to Ben and Roger!