If the majority of your journeys are short and you only undertake longer trips every other month, it is likely that you will experience issues with the DPF on a diesel engine at some point. This kind of journey pattern will not give the car enough time to get up to temperature nor the consistent speed and engine revs required for the DPF to regenerate. As much as annual oil changes will help to a degree, changing the DPF every year would be a very expensive solution. Newer diesels still have DPFs and require the same driving parameters to regenerate.

If a petrol would be too expensive to tax, you may wish to consider a petrol hybrid, which would provide better fuel economy than a pure petrol and should be less expensive to tax.