It has been the site of royal weddings, funerals and nearly every British coronation since 1066, Westminster Abbey is also known as a Royal Peculiar - a church controlled not by a bishop but by the monarch herself. Crowned there 65 years ago, Queen Elizabeth II is now the world's longest-reigning monarch and to celebrate, Westminster Abbey has commissioned an historic new work - a towering stained-glass window. The creator behind it is David Hockney - the California based artist who famously refused a knighthood and declined an invitation to paint the Queen's portrait because he was too busy painting landscapes in Yorkshire. Adopting an art form which is over 1,000 years old and working with glass blowers from Germany is yet another surprising move from an artist whose career has continually defied expectation. With unique access, imagine...follows the whole process from design to installation.