if you need to do the wakefield to Bournemouth trip again I would avoid the M25 at all costs (and the M1 for about 30 miles north of the M25 too for that matter)
It might be worth taking the M1 as far as the A42 then taking that to link you up with the M42, then onto the M40, then A34 towards Oxford and Southampton, from here you can pick up the M3 towards Bournemouth
Of course it all depends on the time of day, but bear it in mind!
ps. flybe also fly to Southampton from Leeds/Bradford. Not sure on the frequency or prices though!