Bluebird Pompey

We are considering the 04 plate 1.4 petrol Desire as opposed to the diesel model. I had a Xantia diesel and loved the car, no problem with it at all, however I thought that diesel was a lot more expensive to buy nowadays than petrol? Also, I'm amazed that everyone keeps quoting £35 tax, is this right?? I thought the gov were tryuing to persuade drivers to move away from diesel and as a consequence everything is dearer. Am I totally wrong?

I'm thinking about buying a C3, and this thread about a/c has been very enlightening. I've never had a/c in a car and didn't realise it should be left on all the time. So my question is... can I leave it switched on and have heat at the same time?