I drive this route a lot. Yep, lots of new cameras along the M1 and M25. They lower the limit past Luton to 60mph for most of the day even when it is quiet. The long 50mph roadworks with average speed cameras between J16 and J19 catch a lot of people, especially the 1 mile of M1 50mph average speed past the M6/J19 construction. Same goes for the 1 mile or so past J21/Leicester services. Cruise control was made for today's motorways.

If I fancy a 'blast' in the evening, or I am driving during rush-hour I use the M40/A43/A5 (but, ahem I did get caught by an unmarked car on the A5 ... oops).