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I have had a company return to readdress a damp problem that won't go away. They came on 21/11/11 and knocked off the plaster again and slopped on a grey substance that I was told was tanking that they use in stubborn damp area like pub cellars. I have then paid a decorator to paint the bathroom in water based, chalky paint to look nice for Christmas. However to my frustration the problem has already started to return. Sections of plaster have bubbled up and gone powderey and I am at my wits end what to do. I have attached images of what it currently looks like and any advice you can give would be much appreciated. They have said they will come back on Friday to have a look but they are baffled too??!! I think they think i'm a bit daft.
The bathroom is downstairs in an end terrace with 3 outside walls. We have over a period of six years had an exterior wall took down as it was suggested that the wall may be drawing moisture from the exterior wall, we have an extrator fan fitted. Our bath is a freestanding bath so air can circulate around it and it has not yet got tiled after 6 years due to the ongoing problem. I have owned the house for a number of years and the company have looked at the problem 3 times, under a 30 yr guarantee.
Thank you

No pictures. But how far down is the internal floor area compaired to the exterior?
Is the ground sloping towards the property?The surface water (rain) may be forcing damp into the property and a land drain may have to be installed.For you to have damp problems of this nature,There may also be an external problem like either a broken drain or leaking water main.

Tried to post picccies but they were too big? I'll try again The room is ground floor. You step outside down a brick height to a patio area. The garden steps down from a patio area that slopes away from the house. We are last in a row of 3 terraces and next door is an old house whose garden is a good 6 ft below ours. Our house acts as a large boundary wall. The pipes from the bathroom are all above the patio, running close to, parrallel to the wall, to the main down pipe and to the main drain.
Thanks for your input :)

It sounds like penitrating damp,whats the condition of the pointing of the brickwork?
If its in poor condition then it needs repointing.If its in good condition then spray the whole wall with a silicone sealant.