Diversionary Routes - Bromptonaut
PU's A14/M11 thread got me thinking about other useful alternative routes. A few starters:-

M1/A50 instead of M6 to Stoke and beyond.

B430 through Middleton Stoney and Weston on the Green instead of M40 to link the A43/A34

County roads via Litchborough/Canons Ashby/Moreton Pinckney/Thorpe Mandeville to M40/J11 instead ogf the A43 between the A5 and M40. This was the pre 1990 route of the B4525 from Northampton to Banbury and is still through signed in places.

Diversionary Routes - Avant
Thanks - I've used the first two of those when Trafficmaster warns me off the motorways in question.

There's also:

Old A33 instead of M3 between Basingstoke and Winchester

From South and West to Cambridge, Bury St Eds and anywhere up the A11 - M25 / A1 / A505 instead of M25 / M11. Best way now they've at last bypassed Baldock, and it seems that the mania for digging up the M11 near the Stansted turnoff is insatiable and chronic. It also avoids a bit of M25, which can only be a good thing.

M1 / A1 / A68 instead of M6 /A74 etc from the South to Edinburgh - a bit slower though not as much as you'd think, and much more scenic.