I got a back to wall (not wall hung) from B&Q for a very reasonable price. I
think wall hung ones are majorly expensive. They're quite an engineering
design problem to stop them cracking.

1. Do they all support a dual flush button ? is this feature dependant
on the cistern I use?

That's about the cistern.

2. If I use a wall hung unit, do I really need a bracket costing as
much as the WC pan itself ?

Yep.

4. So far I have seen ideal standard from plumworld. Any other names or
sites for me to use please ?

I got a back to wall (not wall hung) from B&Q for a very reasonable price
(hazy memories, but I think it was 99GBP). I think wall hung ones are
majorly expensive. They're quite an engineering design problem to stop them
cracking.

Christian.