Tin foil heat reflecting panels behind radiators. Any problems?

A number of years ago the "warm homes scheme" supplied thick silver foil panels to me to put behind the radiators on external walls. I have been having problems with damp walls behind radiators only and suspected a new damp course was needed. Damp behind all the radiators that had been fitted with the foil. Taking the bull by the horns in the worst room I removed the radiator and took all the damp plaster off the wall. Behind it the brickwork is completely dry. No sign of damp anywhere even when I removed the skirting board and can see to the ground. No smell of damp either since the plaster removed. This must have been condensation and I suspect all the other rooms are the same where the foil is fitted. Has anyone experienced a similar problem like this with the foil. Maybe some plumbers can provide the answer.