As you may be aware if the taxable income of either of the partners to a civil relationship or marriage falls between £50,000 and £60,000 the child benefit is clawed back at such a rate that it is totally clawed back if the taxable income exceeds £60,000.
When this charge was first introduced the general advice was to still claim the benefit in case personal circumstances changed as there was only a short limited period in which the benefit could be retrospectively claimed. If however one has opted out of claiming it the time limit was extended to two years so if you wish to claim child benefit for the year ended 5 April 2014 you have until 5 April 2016 to do so.
The election has to be made by the person entitled to the child benefit which of course might not be the same person suffering the charge. If as a result there is then a liability in the year of reinstatement then the return must be amended and the tax is due for payment 30 days after the return is amended.
Interest is likely to be charged based on the original due date that tax was due for the year – in this example but 31 January 2015 but there would be good grounds for challenging.