When political parties accept donations, they are required to check who the donor is but not where the money actually comes from. Panorama's investigation of the Pandora Papers, one of the biggest offshore leaks in history, reveals the financial secrets of three major donors to the Conservative Party. Reporter Richard Bilton asks whether the rules governing political donations are fit for purpose. Update 3 December 2021: Following publication, Mr and Mrs Chernukhin have made legal complaints about this programme. They say that the programme is defamatory of them. In their complaint, they have told the BBC that no deal (corrupt or otherwise) was ultimately concluded with Mayor Luzhkov in respect of the properties in Moscow.