Thanks for all the replys.
Will have to have a go at this again this weekend, work has kept me shattered so far this week and it will be like that till friday.
The plaster and laff* appears to be about 12mm thick, therafter a 2/3 " gap, then brick. I cant see the brick as i have only the tiny holes made by the masonary bit, but i imagine i am hitting brick or stone.
Here's how i went about this so far. Say the first vertical baton is a metre and a half, 1500 mm. I predrill the wood with a small wood bit and create about seven pilot holes, equally apart.The wood bit leaves a marking on the wall which i then use a masonary drill to drill into the marks left by the wood bit, i drill about 5 " deep with the masonary bit. I then screw the wood screws into the vertical piece, add the rawl plugs to the end of the screw then try to get the baton into the wall. This bit is doing my head in, trying to align all seven screws with rawls into the seven holes i made and then try and get them into the holes i made in the brick. Surely there must be an easier way than this, lol.
Hope the above makes sense
Anyway what i am going to try as soon as i get a chance is use screws larger at 120/130 mm and try the above again. Hopefully the longer screws will help me get deeper into the wall and the rawls will manage to grip. Thats saying i can i get them all to line up with the holes in the masonary as i cant see them.
I also have another idea

, lets see how this grabs you. I was thinking of using rips of 3/4 ply attaching these using wood screws to the plaster and laff, masses of screws will ensure i get a good grip on the laff, then add 4x1" to the rips of ply, then secure the MDF TO THE 4X1.. i think as i am only using 12mm MDF this ply/4x1 method may be strong enough to hold the floating wall in place. This also means i dont have to piddle about trying to align holes up and drill the wall to bits. Thoughts on this?
Really appreciate all the replys so far and hope to hear from some of you again, thanks.