First thing is to confirm the presence of mortar on the wall ties. Hire an endoscope with integral light source, drill a hole through the inside wall about 50mm above a damp patch and have a look.
If there is mortar sitting on the ties it must be knocked off and this is not a simple task. You may be able to get at some of the ties if you can get access to the top of the cavity and it is open.
If your cavities have been filled with insulation removal and rebuilding the outer wall may be the only solution.
If your house was built in the last 10 years you may be able to persue a claim through NHBC or whoever guaranteed the build.
Not good news either way - a major problem.
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