Mr Plasterur

You will need to dig foundations for the brickwork which would normally be 100-150mm thick , usually 450mm below ground level.

The problem with cellars is penetrating dampness caused by the water pressure in the ground acting on basement walls , if a wall feels damp then it will still be damp no matter what board you use. Before you board out the cellar i would recommend that you get your cellar walls tanked , theres many systems available including trowel applied systems i.e. a plasterer could apply these systems cheaper than a more traditional preservation company(who would employ a plasterer to do this anyway).

Depending on system you could then either dot and dab walls with plasterboard or build freestanding partition keeping it clear of wall and board it out.

This might sound costly but cheaper than converting cellar then having to rip out walls due to dampness , u could apply the tanking system yourself if you are handy with a trowel or look around for a system which can be applied in thick brush coats(used system before with excellent results but cant remember the name just now)

Hope this helps.