I remember as a child every time I went to that area sitting in massive traffic jams for hours to get home. I take it it is still like that and I would be better off getting the train. Has anyone driven it recetnly?
I drove from Basingstoke to Dorchester last Saturday and the traffic was fairly slow but moving. Would usually take about 1hr 45 and took 2hr 15 last week. Lots of people heading to the coast with canoes on their roof-racks!
I have been making this trip for 20 years, it is nowhere near as bad as it used to be (Winchester by-pass ... shudder).
Until the schools break up it is usually OK. You will get the worst of it leaving at that time though. I usually come off the M3 for the A31 to avoid any M3/M25 silliness, but then I am on the A3 at the top end anyway.