If you mean the shot with the Metrobus, that was just me messing around. The M1 is done as a track though, so the sections where it runs alongside could be driven using BRR, but it's only between the North Circular and Scratchwood, and a short bit at Sundon between Leagrave and Harlington.
The M1 actually takes a very different route between those two points though, swinging west towards Watford and Hemel Hempstead before passing Luton, and then after briefly coming alongside the MML it again goes off west towards Milton Keynes whereas the MML heads slightly east to Bedford, infact, from Luton it's the A6 that follows the line closest, right through to Ambergate north of Derby where the line turns east then north towards Sheffield wheras the road follows the old Manchester route, now closed between Matlock and Buxton (incidently, the road then follows the WCML to Carlisle).