I only use my credit card when out and about (except when I'm in a pub, where they don't accept them).
The reason is very simple. Petrol is expensive, and I use lots of it. I'm hardly going to drive around with a few hundred quid in my pocket to spend on fuel, particularly in London
I also don't have a debit card because mistakes are not very easy to rectify when you're money's already gone...
Like if your debit card is double swiped, or cloned you can kiss goodbye to the money in your bank account. If, on the other hand a similar thing happens to your credit card the credit card company picks up the tab and it tries sort out the problem.