When the M40 first opened through, without services, diversions at High
Wycombe to Asda, Banbury to Tesco and off the M42 to various filling
stations on the cut-off from J1 to J4 on the M5 were convenient and are
still cheaper than the service stations.

Coming south, a turn off at J2 and heading for Slough found another Tesco
store on the A4. Back to the M25 at J14, or the M4 at J5, depending on the
traffic.

Surely that'd be Junction 1? (down the A412 to the Tesco that used to be the
Co-op, no?) ?

If going clockwise round the M25 and wishing to join the M4, a diversion
up
the M3 to Bracknell, and then via the A329M to the M4 is shorter and
quicker, and passes Sainsbury's in Bracknell en route.

Not only that, but there's a new Sainsbury's local at the Shell garage,
which is consistently pretty cheap for fuel these days (I've filled up there
at 79.9p/l for diesel when a lot of other places have been 3-5p more).

Peter