Paul Terry ) gurgled happily, sounding much
like they were saying :

Good point - of course it couldn't work at J11 (motorway:motorway
only), but any obvious reason they couldn't do something like that for
the A3 junction?

If you mean signs to the A3 Ripley services, the reason is likely to
be that you cannot easily get back to the M25 without a long
deviation.

So either redesign the access to Ripley services, so you *can* turn round
there, or take 'em in towards London, to the big supermarket just off the
first junction, the A245 at Painshill - only a mile or so in and nearer
than Ripley.