At the event? It needs a bit of planning TBH. Lots of it but split Transition means your car is at T1 about 2 miles from the finish. Options are cycle back to your car along the road (with bags and wetsuits around your neck) or take the water ferry which I did not want to wait for. Or have a sherpa park at the Finish (easy) take all your gear for you and cycle back to T1 without all the clobber (what I did). They may of course have a different system in 2013
If however you mean parking at the Premier Inn Marlow I have absolutely no idea!!!!