definitely not at such low mileage.
I do about 18-20k a year. My BMW & Saab were both diesels, 42mpg at best on the combined urban/motorway commute. 60 litre tank at 140p/litre at today's prices, £84 per tankful. 8 days from fill to fill, 550 mile max range, typically 520.
I'm now driving a Citroen C4 1.6 petrol, getting 34-36mpg; 50 litre fill up at 130p/litre, £65 per tankful. 400 mile max range, 6-7 days between fill-ups.
OK, that extra £19 goes a further 120 miles or so, but I bet it evens out over a year. Yes the diesels were cheaper to tax, but more expensive to service.
Even at 20k miles a year I'm not sure diesel is significantly cheaper to run than petrol, not on an older less efficient engine anyway. Less than 10k a year & petrol almost certainly a better bet