Train
tbh, looking at the fact you will be within walking distance of work for the few times a year you will use the car the cost will be a lot compared to the discomfort of a train now and again.
With a car you are going to have the outlay, say £600 for a small runner, £600 insurance as a rough figure if not more, running costs including Tax £125? MOT £45 Service £100 that's without the petrol and any breakages during the year.
One huge plus for a car mind is the freedom having said all that above i wouldn't trade mine back for cycling or walking.