It is not usual for infrastructure trains to run on Saturdays but in this case, the 14.53 Bescot to Wembley Yard was sent south as 6G52 in preparation for overnight engineering works in north London. Interestingly, I also saw 66770 on an infrastructure working at the same location over a year previously but heading north on that occasion, see.....
https://www.ontheupfast.com/p/21936chg/28612412204/x66770-13-15-milton-keynes-central