Not a B&B but my best Grayling fishing has been on the Whitewell beat of The Hodder. Only access for members and a residents at
The Inn at Whitewell. Follow the link 'out and about>Fishing' for details. It was Spring and I was targeting Trout but picked up three nice Grayling, two to a GRHE under a Klink and one to the Klink. The best was around 17 inches, the smallest about 11. I also caught plenty of Brownies, a couple of wild looking escapee Rainbows and a few Salmon Parr.
It's a fabulous hotel, great food and beer, not cheap but priceless memories! The Slaidburn stretch further upstream is available on a day ticket.
Also
The Red Pump Inn is just downstream and a lot cheaper, a food pub with rooms but also some river access. I haven't fished it myself yet but would love to.
SharkeyP