They have to have a good, genuine reason to sack you. What reason have they given? The reason you have posted is not a good enough one. Check your contract and terms of employment for the finer details. If they want rid of you, can't sack you for gross misconduct, and there is no other get-out in their terms, I would advise waiting for them to make you an offer to leave. This happened to my husband recently, and although he would happily have told them to stuff it, he didn't, and they had to come up with a decent payment package including money in lieu of notice and all holiday owed. He was being bullied too, they all denied it too, but if you resign, you're doing them a huge favour and saving them money. Sit tight, keep doing your job professionally and wait for them to come up with the goods. Oh, and remember that if they try to persuade you, insist they include a good reference in the 'leaving' package!! That way they can't scupper your chances in the future.
Good luck!