As far as other running cost go... servicing should be very slightly higher for the petrol car due to the spark plugs renew at 4 years. But, when things go wrong, diesel engines can generally be more expensive to repair than petrols, especially any elements to do with the fuel and air supply systems (try diesel fuel pump...). Also, diesels are more prone to suffer terminal engine damage as result of mis-fuelling (petrol in diesel engine) or overfilling with oil ('runaway' engine). Said that, you could get mechanical breakdown cover, and on a good car this will not be an issue anyway.
Also, the diesel will cost more to buy, so if buying a petrol car you may be able to get newer model or better spec for same money. But then again the diesel will be easier to sell on and you will get more for it when you do.
On another note, in the past diesel cars used to be lower on the insurance group than their petrol counterparts, though I am not sure if this is till the case nowadays given that diesel engines have become quite powerful.