Beenz for one you can buy an electronic damp meter for not alot of money.
Fact - rising damp is never above 1 metre high.
Old methods of injecting the brick work doesnt really work.
New methods are , a special gel u inject into the mortor joint ( every 75mm )at damp level ,
The gel uses the moisture in the morter to travel along the join , creating a very good damp seal.
Also knock of the plaster to 1 meter high , do the same thing with the gel on the inside course.
Then when you replaster using sand and cement with a waterproofer additive.
This should sort out the problem , and if you have a builder pal , doesnt have to cost the earth , if the house is right for you , dont be put off by a bit of damp.
Plaster moisture levels can be affected by not having heating on in the property for a few weeks.

Good Luck.