I have started to go out with the local 'Rollerski' club in Manchester and I have found the best place to skate in the UK (possibly).
The Chester to Shotton Cycle Path.
The route follows the River Dee and is 32km out and back from the start. The path is flat, super-smooth and picturesque. The route actually carries on along the North Wales Coast to Colwyn Bay so a tour is possible.http://www.therollerskidirectory.org.uk/
The rollerski club has also put together a series of routes that are skatable throughout the UK. The list is under 'Regions'.
Finding a good place to skate is the toughest aspect of inline skating and this list is superb.