I'm also in Portsmouth. Render is rarely applied to older walls that are sound and dry, unless there is some decorative intention. Render is however, often applied when dampness is already present, and may cause further damage to the structure and dampness problems inside if the true cause of the original damp is not remedied. If render applied in the past is cracking and falling off, then re-rendering may not be a permanent solution.
What sort of walls have you got, what is the thickness (measurement made on an external wall where a window is located), and when was the property built?
Where's the internal dampness present?
Some photos, inside and out, would be of use to diagnose the reasons, and suggest a course of action, which may be less expensive and more effective and permanent than a return to the status quo.
For instance, the later Victorian and Edwardian housing stock around here was built with unfilled cavity walls, to protect the inner leaf of the wall from the sort of incessant driving southerly/southwesterly rain that has characterised this winter's weather. These walls were never intended to be waterproof, but weather resistant, and capable of shedding the majority of the rainwater, and drying out later. Sadly, the available wall ties - black japanned wrought iron fishtails have rusted over the last century causing horizontal cracks in the mortar joint, as the rust expanded in the bedding mortar. There may be associated structural instability.
So, if any of the cracks in the render are long and horizontal, there is a need to isolate the remains of the wall ties from the outer leaf of brickwork, repair the crack, and use stainless steel wall tie replacements, before considering any further action.
