Why not try Acas, I once did and they were able to tell me over the phone where I stood The link to there page is
here and has the national phone number as well as more links.
Just as a matter of fact, at my old place of work one of the guys to ill on holiday and came back to work and changed his holidays to sick days ( twice )
I on the other hand went to France for the day when on the sick and got slated for it, so maybe it's the timing, I dont know but give Acas a call as I said.
Good luck