I know what you mean, I have had to use the Leon as the Zed is going to Abbey on Monday to have a couple of things sorted out and I don't want to use it till then....
I have seen that the Leon shows a minimum of 38mpg even on 3-4 mile trips... so if you only had a short commute you would still see a decent saving if you have a diesel.
Also if you do get a diesel it may be more expensive initially but will hold its value a bit better