Damp issues - help!

[WhatWillSantaBring]

So we have a ground floor flat in a Victorian mansion block. For ten years, we had no issues at all. About five years ago, we started getting terrible damp in the bathroom - this is where the main water pipe for the block runs and it started sometime after they'd done some work on the water in the building. We got them to investigate and the plumbers report came back stating it was condensation from the shower. Now the damp has spread to another room.

I don't trust plumbers generally (I know there are good ones, but I don't know how to find them - any recommendations for Zone 1 London gratefully received!). I want the issue fixed once and for all, but have no idea how to go about it. If it's an issue caused by the mains water pipe in the building, then I'd need proof so i can get the management company to pay. If it really is just condensation then what can we do?

There are specialist leak detection companies - for £500 they worked out where a leak in our house came from after MANY different people had come up with all sorts of wrong answers - to be fair it was really hard to find. Our home insurers required us to use them (and didn't cover the cost) but it was worth it.

Alternatively, get an Independent Damp Surveyor. You can find them in your area on the Property Care Association website. Just make sure they are 'independent' and not part of a damp proofing company. They have nothing to 'sell' and not interested in getting you to sign up for building work or damp treatment. They just show up, do a survey and tell you what the problem is and how to fix it. It's up to you what you do with that information and who you get to do the work afterwards.
Friend of mine recently had quotes from builders for thousands of pounds worth of building work to fix her 'damp' issue. She got an independent damp surveyor in to look, he identified the issue as condensation and now she's making a few 'lifestyle' changes, (less clothes drying on the radiators) and a couple of extractor fans installed in the bathroom and kitchen. Her logic was it was better to pay a few hundred for the surveyor and the fans in the first place and then see what effect that has, before spending thousands on possibly unnecessary building work.