Need a pit stop between Cambridge and Southampton

[needapitstop]

...suitable for a quick dog walk. Bonus points if it has good coffee/cake. Gold star if it sells plants.

I'd aim for Colne Valley Regional Park

Lightwater country park, J3 of the M3 - not sure what their cafe is like.

Runnymede, J13 of M25 - national trust with a tea room.

Or if you don’t mind a little bit of a detour, Dorney Court (good cafe and garden centre) is near J7 of the M4 (you could cut back down to the M3 on the A322, or continue on to the A329 or A34 to head on to Southampton)

Thank you both, that's really helpful.