Once again thanks for all the replies.
I intend on getting the train to Swanwick and getting a taxi from there. My train gets in with about half hour to spare before the tests start so should be plenty of time. Will make sure I have some taxi phone numbers should there be none at the rank.
Getting to Southampton from Guildford is a pain as you have to double back to Woking to get the right line. Think I will give it a miss as there are too many variables to go wrong.
Cheers again guys, much appreciated