I could be completely wrong about what I about to say so forgive me if I'm wrong but I assumed that a diesel engine would give me better results over short journeys like those above?!?
The "torquey nature" of the TDI was also a pleasant change from the high revving NA engines I've had in the past.
On short trips your diesel engine would have the same economy issues as your petrol. + short trips are not good at all for your DPF, which is not particularly cheap to replace.
Then you add the rest of potential diesel problems - DMF/EGR/turbo/injectors all of which don't like short trips.
I for one hate petrol engines that you have to rag to bits to get anywhere - clio 172, civics etc, but the solution is not diesel.
The solution is a decent petrol - either something with a bit of displacement or one of those small turbo petrols that you can find everywhere. The later won't be as reliable as the first, but should be better than a diesel without the tractor noise. Have a look at something like the 1.4 tsi.