So overall... Is the D40x worth that extra £70?!
Unfortunately, only you can answer that question... 10 megapixels do not mean only larger prints - they also give you more flexibility in cropping... do you plan on shooting a lot in low light? - the D40 has cleaner high ISO pictures... and finally, a thing that just came to my attention - do you expect to take images with powerful light sources (like the sun)? - you might get blooming with the D40 due to the way its shutter system was designed (both mechanic and electronic).
So you need to think how important are the differences for you, and then you'll know if they are worth those extra pounds...