Animal charity PDSA last week revealed that it had seen a big increase in the number of crimes against its shops, including shoplifting. One store even had the letter P stolen from the sign on its shop front. The charity said its shops were seen as an "easy target".
Lekha Klouda, director of the Association of Charity Shops, said measures to beef up security in large shops had pushed petty criminals into targeting smaller businesses.
"There is no doubt that there is a group of people out there who are smart enough to work out where they are most likely to be successful," she said.
She added that charities do not have the resources to install the most up-to-date security systems.