This might sound like an old joke but it does depend where in London you're starting from - but give yourself 2 hours, that will allow for traffic jams etc.
with good traffic, it usually takes 1hour 40 mins, so give yorself a couple of hours, as you will have to go through the centre of southampton to get to the ground.
Hi there, we live in Brixton and my husband is a Saints fan, it can take him from South West London. 2 - 2.5 hours. If the kids are off school then it's much better getting through. Suggestion - maybe the M25 then M3 ?