The tax office has admitted singling out people with dual nationality for extra checks, and 11,000 people were subjected to more stringent screening because of this, broadcaster RTL said on Monday.

This is the first time that the tax office has confirmed that it did use dual nationality as an ‘indicator’ of potential fraud, and could suggest why most of the families caught up in the recent childcare benefit scandal had ethnic minority backgrounds.

The tax office confirmed to RTL that in 2012 it built a risk assessment programme which used five criteria based on ‘knowledge, expertise, patterns and the experience of earlier years’. Claiming high tax deductions was also a trigger, alongside dual nationality.

In 2014 and 2015 the law was changed so that local authority registers no longer included information about dual nationality but the tax office continued to use old lists, RTL said. The Dutch privacy watchdog AP is currently investigating.

MPs Pieter Omtzigt and Renske Leijten, who have long campaigned for the rights of families who lost money in the childcare benefit case, said they now want answers from ministers about how long this has been going on.

‘This is extremely serious… and a smack in the face of society,’ Leijten said. ‘We were promised things would be cleaned up but now, after all this time, this comes out.’

Last week MPs had asked the tax office to provide details of how it selected people for extra checks but were refused access, RTL said.