I don' live in N.England so never tried any (yet) I live in South England and since I been I been MTBing 8 months, I now know too many rides I hv time to ride by using the flwg :
Mountain Bike Rider (MBR) magazine has routes every Month, so does What Mountain Bike magazine.
You can also just go onto a search engine and put 'MTB routes' there are lots of sites with routes.
Also on Amazon you can buy MTB routes for different parts of England - they are good - you will also need to get a OS landranger map for the area you will choose to ride.
Your lucky yr in the North there are so many great looking routes up there - Pennines, Dales, Lake District, list goes on I guess...