What plasterboard to use... Insulated or not?

I'm renovating a 110year old end terrace. Plaster is all off right back to brick and I'm re plastering myself when the time comes. I took a professional quote and the contractor said that for the external facing walls, because I've stripped it all back, I'd need to use insulated plasterboard to conform to building regs??? Is this true? If so what is the minimum standard?