I do not accept that there is any anomaly in the tax treatment of single, separated and widowed parents. The differential in the tax treatment of individuals on the basis of their marital status arises in large measure out of the Supreme Court Ruling in the Murphy case.
Single persons and separated persons being taxed independently receive a single person's allowance of £2,100. Where these are parents living alone with dependent children, they are entitled to a one-parent family allowance of £2,100 bringing their total basic allowances to the level of the married couple's allowance of £4,200.