TV licence collectors have “fallen short” of the standards the BBC expects, the corporation’s director general has claimed following reports that they are deliberately targeting vulnerable people who have not paid.

Enforcement officers at Capita are ordered to catch 28 evaders every week and promised incentive bonuses of up to £15,000 a year, according to a newspaper investigation.

The company is reportedly paid £58 million a year to collect licence fees for the broadcaster, and its staff were said to have targeted vulnerable people, including a war veteran with dementia and a young mother in a women’s refuge.

In a letter to Capita’s CEO Andy Parker, the BBC’s Tony Hall expressed his “serious concern” about the reports and called for “urgent clarification and reassurance” that vulnerable people were not being “targeted”. He wrote: “Enforcement is clearly important for public confidence in the licence fee system.

“However, it must always be carried out in a way that is fair and reasonable. In particular, it must deal sensitively with vulnerable people.

“There is a very clear Code of Conduct that sets out the BBC’s expectations from Capita. It is vital that your Enquiry Officers adhere to it and conduct themselves to the highest of standards.

“Public trust is the cornerstone of the licence fee system. It is clear that, in this instance, Capita has fallen short of the standards the BBC has a right to expect on behalf of the British public.”

Downing Street said ministers would be raising the conduct of the enforcement officers with the BBC.