Parents should think carefully before making use of a new government childcare offer, says the TUC.

Under rules which came into force on Wednesday, working parents can choose to receive up to £50 a week of their salary in childcare support.

It would mean that they will no longer be paying tax and national insurance on that part of their pay packet.

The union organisation said those with the option of taking up such a scheme should weigh up whether or not it makes financial sense.

Parents need to be aware that when sacrificing an element of their National Insurance and tax to pay for childcare, there may an impact on their current entitlement to tax credits, said the TUC.

And there may also be an impact on any future entitlement to work-related benefits such as maternity pay, sick pay and occupational pensions, and to state benefits such as the state second pension, Incapacity Benefit and Job Seekers' Allowance.

"The government should rightly be proud of its record on investment and support for childcare," said TUC general secretary Brendan Barber.

"Today's changes are another good example of their commitment to help working parents.

"Many people, especially higher earners will be quids in as a result of these tax and National Insurance changes, but parents should do the sums first as not everyone will be better off.

"Parents on low pay may find that by signing up they will be short-changing themselves further down the line."