Bathroom ventilation: dMEV system advantages?

[notsothuggie]

A friend has a small flat (35m2) and the bathroom is suffering from condensation problems from the shower/bath. A company specializing in "damp problems" has inspected the property and, aside from the outside wall needing to be repointed in places and the gutters realigning by the freeholder, has recommended my pal installs a decentralized mechanical extraction ventilation system.
The current extractor is a decent one - wall mounted, moving the damp air to outside the building. However, this is proving ineffective and mould is appearing in the corners and on the (paper-lined!) walls of the small room.
It's difficult to find evidence of how this system would be preferential over a more efficient extractor fan. And, the price quoted is huge - £580 (including installation). We also think this would make the flat freezing cold in winter if cold air is being constantly circulated inside.
Eventually, he would like to tile the whole room, but until the source of the damp is eradicated, there seems little point in doing so.
Any advice would be most helpful. Apologies if this is posted in the incorrect area.
T.

 

[endecotp]

How does he dry his washing?
Does he actually use the current fan?

 

[notsothuggie]

Can't rule out them drying washing (but think the problem would be even worse if they do). The fan works and they switch it on after showering. Apparently the recommendation is for ventilation with a humidistat, which makes more sense as it would then switch on automatically when the % of humidity is at a certain point. But, having "googled", we can't find one to substantiate such a high price.