This is where chemicals have been injected in to the wall fabric as an attempt to stop internal dampness.
This is a very controversial subject and an issue that would definitely require Listed Building Consent. An application for Consent is unlikely to be granted and there are almost always alternative options that can be considered. The essence is on breathability of the wall and not simply as assessment whether it is dry or not. It can be a complicated subject and the use of lime mortars, lime plasters and lime renders will be very beneficial to helping the building to breathe. Please ask me for advice before undertaking any remedial damp treatments.