You may not need a damp proof course. When buying a property a mortgage surveyor will put his meter on the wall and the minute it beeps he will ask for a damp report. ( to cover himself) a lot of companies use this excuse to put in a damp proof course which is largely unnecessary.
Depending on the readings, the dampness could be due to penetrating or lateral dampness, interstitial condensation or even a plumbing leak and a damp proof course will NOT address these issues ( but will mask it for a year or so) .
Also most homes have some type of dampness and as long as it isn't causing a problem It is liveable with. Beware the free contractors who advocate a quick spurt of cream in the wall to cure all ails.