there's a good article here
follow MIDRIS article by Dianne Garland
After a a bit of a fight (registrar was adamant MUST have CTG, NOT allowed water) I spoke to the consultant who agreed that I could use water pool for the first stage for my VBAC, but we agree I would get out for second stage or if any sign of trouble (whether there would have been time or I would have been "able" to get our is anogther story of course!)
Also some hospitals have waterproof/wireless CTG (not that I think, on balance, that CTG is helpful for VBAC, but that is just MY opinion )
Long story, but I ended up with an el c/s at 10days overdue instead of my planned VBAC, but if DS had have got his act together & got moving he would have been a water birth