There is the Sutton Scotney service station on the A34 approx 7 miles north of Winchester/M3 junction 9. Or a Mike P says there is an "industrial estate" just off Jctn 9 of the M3/A34. Tesco's huge car park could be a psooibility, but watch the height barriers!! - turn into Tesco's and use the first car park entrance/exit immedieately opposite the Tesco petrol station and park up in this area and you shouldn't have any problems. For info Tesco's is open 24/7.