I am currently working on a project renovating a building which does not have a secondary fire escape access to the 1st and 2nd floor. The stairs are timber but also have gloss painted walls etc. The main shaft we want to use fire retradent varnish on, and fire retardent paints an well as door closers on all the doors leading onto the central shaft, as well as emergency lighting. Do you know of any suppiers who supply paints and varnishes of this nature.

Also, we have a Blackfriars Polyurethane water based varnish and it says it is heat resistant. Would this be plausible to use to over coat the existing varnish?

The staircase enclosure is part of the circulation area and is required to be a low fire risk, consequently a sterile area. All surfaces, walls and ceilings should meet a "Class 0: surface spread of flame" standard which means any varnish or paint you apply should meet that standard. When you purchase the paint or varnish the information you receive from the manufacturer should state that when applied in accordance with the manufacturer instructions it will achieve the above standard.

If you contact the supplier or the manufacturer of Blackfriars varnish they should be able to inform you if it meets the above standard and how it should be applied.