Are you referring to UK National Insurance contributions? I've never paid both UK and US contributions and, AFAIK, since the US and UK have a totalization agreement in place there is no benefit in doing so. What advice did Andy receive on this ?

AFAIK, there is a tax treaty in place between the 2 countries in terms of income tax. Andy checked with the DHSS and the Inland Revenue as to what he needed to do to ensure that his status remained "paid up" for NHS and pension purposes in case we decided to move back.