This is one of my favourite films and a rare example of the film being better than the book - although it probably helps that JJ Connelly wrote the book and the screenplay. It's a film with loads of quotable lines 'You give a bleedin' asprin an headache' being one of my faves.
It's also a great snapshot of London just before the city started getting tall. When they're at Greenwich Park you can really see the difference between the city skyline then and now.