I'd seen this question but, with so many replies, I assumed that it had already been answered. Here's my input anyway:
Dead easy!
Mr S takes a Bakerloo Line train direct to Marylebone, where he catches a train to Beaconsfield. (There are 4 direct trains per hour, taking between 20 and 30 minutes for the journey).
Smow takes the A23 down to the M25 and then clockwise around to Jn 16, for the M40. She leaves the M40 at Jn 2 and follows the signs into Beaconsfield. (It's dead easy to find the station. I've worked there, carrying out a travel survey, so I know that you can't really get lost and that it's got a massive car park. The postcode for satnavs is HP9 2PJ).
Having picked up Mr S, Smow returns to Jn 2 of the M40, following it to the end (which is Jn 3A of the M42). From there she follows the M42(N) signs. After that she take the M6 Toll Road and then the M6 to Jn 15, where she joins the A500 into Stoke-on-Trent.