8x10 with my Fuji W 210mm lens. No filters. I posted up the same question on facebook and was given a few things to check - if the lens was mounted correctly, which I can confirm it is, and also to check my developing tank - I did that and it seemed to be fine. I'm going to develop a single sheet of unexposed film this weekend and see if perhaps the box of film has managed to get some light into it (hopefully not though).
It's quite frustrating and at the moment it's proving a bit difficult to nail exactly what the cause it. I'm shooting with new film and developing with new develop and a new lens but my developing process hasn't changed a bit, I'd be surprised if the lens is at fault but I guess it could be. I'm going to shoot a sheet of film with my Fuji 300mm, which I know to be good, and see if I can replicate the issue (or hopefully not).