I'm moving house fairly soon and the one I have just bought means I will have to commute about 7 miles each way to the train station to get into London. I want to buy a cheap smoker to do this but with the short journey each way will it still be more beneficial buying a diesel over a petrol or will the extra of cost of diesel per litre make it uneconomical knowing the diesels are better on long runs? (would go for 1.8 petrol or similar if not).

Cheers