You say mostly short journeys bar a run for about 6 miles or so each week. I suspect your main issue is the length of your journeys. If they are all 6 miles or under, you can expect your fuel consumption to be on the high side, as a) you are predominantly driving the car with a cold engine which will use more fuel, and b) driving around town, albeit "pretty conservatively" with stops, starts and gear changes, is also going to use more fuel than a sustained run at a constant but moderate speed compatible with a gear using low rpm from the engine.
A relatively modern diesel car with emissions control technology is I'm afraid also totally unsuited to your usage pattern. They are only really suited to journeys with plenty of driving at a moderate to high rpm over uninterrupted journeys of 20 minutes or more with little slowing or stopping. More info in the post below, but a petrol engine (or electric/petrol hybrid) would be much better suited to your usage.
Taking the car for a 6 mile journey is achieving nothing. It really needs a regular trip of preferably around 50 miles or so, but at a minimum about half that, to fully warm up and spend some time operating at optimum efficiency. The journey should include at least 20 minutes or so of uninterrupted driving at moderate to high rpm to provide the optimum opportunity for activation and completion of the DPF cleaning process, which is automatically activated by the car as required, but only if the conditions for its initiation and completion are met by suitable driving conditions. I would do that at least once a month as a bare minimum,
Hi I was wondering if anyone has had the same problem as me. 2 Weeks ago my car went in for full MOT/Service. My car failed the MOT on emissions and im told it needs a new DPF. The problem is. The dealer cant get one because Volvo GB havent any, I have contacted Volvo Uk and they say the same...