I've been having issues with hitting middle C and B. I can play higher no problem but when those notes come up no sound comes out. Oddly B is a little easier but still fails often.
Could this be an issue with my pads or am I more likely doing something wrong?
It's odd because lower E and F work which makes me think it's not the pads.
I've checked that I'm not moving my fingers off the holes and I've tried compensating for the slight extra tilt on the clarinet, I've also tried blowing harder.
When the notes do work I can't see that I've done anything different.
One thing I have noticed which I have no idea if it's normal or not is my reed gets very wet very quickly. So i have to regularly take it off and dry it as the sound gets progressively worse. No idea if that related but thought I'd include in case

Any suggestions really appreciated.

If the little finger low F & E keys are not well regulated the E can sometimes sound OK but the upper B is hard but the F & C should be OK. Another possibility is that the regulation of the link key from lower joint to upper joint might be a bit too tight so that the pad on the lower joint ring doesn't quite close - this can cause problems on various notes unless you use high finger pressure. A quick check over by a good technician should reveal if it's a mechanical probem which is usually quite quick to remedy even if one or two pads need renewing.
Another possibility is that you are using too tight an embouchure and/or too soft a reed combined with not enough air support for the notes above the break which can choke those notes.
Good luck.