It's Only a Theory

The guest celebrity is sports presenter Clare Balding and the experts are Dr Aubrey de Grey and Lucy Beresford.

Andy Hamilton, Reginald D Hunter and Martha Kearney decide if experts' theories are valid.

The guest celebrity is broadcaster Kirsty Wark and the experts are Dr David Bainbridge, Professor Chris Budd and Professor Stanley Wells.

The guest celebrity is broadcaster Clare Balding and the experts are Prof Geoff Beattie and Marcus Chown.

The guest celebrity is broadcaster Martha Kearney and the experts are Julian Richards and Dr Peter Thompson.

The guest celebrity is Vince Cable MP and the experts are, once again, Dr David Bainbridge and Marcus Chown.

Clare Balding returns to the judge's chair, with experts David Ryan and Marcus Chown presenting the final theories of the series.