Best way to plaster this internal brick wall?

[Renovirgin]

The back wall in this room of my house had damp issues when my parents lived there. The roof had been leaking and the pvc window was damaged. The rooms were always cold because they didn't use the heating so condensation as well.
The house was re roofed some years ago and I replaced the windows and painted the exterior in Dulux Weathershield last year. The exterior render is in great condition anyway.
The plaster inside was blown so it's been hacked off back to brick. The walls have black ash mortar.

Obviously the wall is damp from years of water ingress and so I'm running the dehumidifier to speed up drying. I don't want any fresh plaster failing due to residual moisture.

My partner, who was a plasterer for years (and whose judgement I trust) says that I need to leave the wall until it's dried out. Then it can be repaired and plastered. A builder who visited recently said I dont need to wait. I can just put up a new stud wall with an insulated cavity and waterproof membrane and that's 'bulletproof.' Apart from the fact this takes up more space, I thought old buildings need to 'breathe'?
Any thoughts?

 

[Wayners]

Phone council building control and take care it from there. You can waste money doing the wrong thing so be sure that it a correct spec then you can get prices for work

 

[Alastairreid]

I would listen to your partner.