HMRC are amending our clients tax calculations to add Marriage Allowance of £212 to the tax liability, rather than subtract it. Apparently this is a known problem but no date was available for this to be corrected when I last managed to get through on the Agent dedicated line. This is not acceptable.
Janette, HMRC has advised us that a fix for the issue you describe will be in place by early October. See our news item Marriage allowance and self assessment – an update on systems problems for a fuller update. It is disappointing that the systems changes for Marriage Allowance were so poorly implemented and that it has taken HMRC to long to recognise this.