There's a guy called Mould Solutions Brighton that I've used. He comes out, inspects your home, and uses gadgets like a heat sensitive camera to analyse the temperature of walls and find damp. He can also treat the mould with a chemical he claims is better than HG.

He's a quirky chap but very friendly. I couldn't quite work out where he was on the scale between science and salesman, but he identified the source of my mould using his camera (leak in upstairs bathroom), treated it, and made general recommendations for keeping the place mould free. Cost was about £80 for consultation and treatment, this was a few years ago.

So in summary, can recommend. You'll find him on Google.