"If their employer is not paying employers' National Insurance, unbeknownst to them they may not then be entitled to statutory maternity pay if they become pregnant, they may not be entitled to statutory sick pay if they fall ill, " he said.

BBC: Tax loophole for UK businesses set to close

Mr Alexander said around 100, 000 employees - mostly teachers, nurses and oil and gas workers - were believed to be paid through offshore payroll services set up in tax havens such as Jersey and could be ineligible for statutory sick pay, but completely unaware of that status.

BBC: Tax loophole for UK businesses set to close