MSE News: Government: 'We can't afford mass tax write-offs'

Amidst all the rhetoric about the recently revealed personal tax underpayments coming from shortcomings in the PAYE system I have not seen anyone spell out that the claims for underpaid tax now being sent out may themselves be incorrect due to lack of information.
These underpayments were apparently generated by failure to adjust PAYE codes for additional income sources, for example where an employee receives a taxable benefit from their employer eg. gym membership or private health insurance. Other possible causes are where a taxpayer is subject to higher rate tax on bank interest or dividend income which has not been allowed for in their PAYE code.
But there are also possible reasons why too much tax may have been deducted through PAYE through no fault of HMRC or the PAYE system. Taxpayers who do not submit self assessment tax returns but who pay personal pension contributions or make charitable donations under gift aid often assume that they have received full tax relief at source for these payments. In fact they have only received basic rate relief and if they are higher rate taxpayers they need to notify HMRC of their payments so that their tax bill can be adjusted.