I'm having the same problem but I don't want to change. My dad was looking at 1 series (but he wouldn't buy a diesel) as he's changing his car around easter time, so I was doing a bit of research for the tax of the petrols;
116i- £110
118i- £120
120i- £140
The fuel economy seems to be good on the petrols from 35-40MPG. Hope this helps