With the competition hotting up, our seven remaining amateur artists head to the world-famous National Portrait Gallery in London and face two portraiture challenges as they fight for their place in next week's semi-final. Portraits are notoriously difficult as everyone can tell if the human face looks right or wrong, so there is nowhere to hide if they want to secure their place in the competition.They first have to produce a self-portrait that is not only a realistic representation but also conveys some of their character and emotions. For some, unsurprisingly, their main emotion appears to be fear, particularly as judge Daphne Todd OBE is a world-renowned portrait artist herself. The mentors, Pascal and Diana, are on hand to guide their teams and help keep the nerves under control.The pressure is then ramped up another few notches as they are presented with undoubtedly their hardest challenge so far. The artists are given just five hours to produce a portrait of a celebrity sitter, something that an established artist would take weeks, if not months, over. Pascal's team must paint the inimitable Angela Rippon OBE, and Diana's artists have to capture the indomitable Baroness Floella Benjamin. The tension in both rooms is palpable as the artists struggle to translate such familiar faces, and many very nearly crumble.Who will be saved by the public panel, and who will the judges take through to next week's semi-final?With Mariella Frostrup and Rev Richard Coles.