Harriet Harman has claimed that by accepting a donation from Janet Kidd (which really came from David Abrahams) in good faith, she has complied with the law, so it's worth remembering what the law actually is on donations. I quote from the Political Parties, Elections and Referendums Act 2000, section 54:
(1) A donation received by a registered party must not be accepted by the party if—
... (b) the party is (whether because the donation is given anonymously or by reason of any deception or concealment or otherwise) unable to ascertain the identity of that person.
Now Harriet Harman claims she did not know that the donation was on behalf of Mr Abrahams - so this could get her off the hook in any police investigation, or will the police and CPS argue that this section requires her to ask the most basic question to a donor, namely "where has this money come from?".