http://www.bikehub.co.uk/featured-articles/cycling-and-the-law/
The salient points:
On 1st August 1999, new legislation came into force to allow a fixed penalty notice to be served on anyone who is guilty of cycling on a footway. However the Home Office issued guidance on how the new legislation should be applied, indicating that they should only be used where a cyclist is riding in a manner that may endanger others. The then Home Office Minister Paul Boateng issued a letter stating that:
“The introduction of the fixed penalty is not aimed at responsible cyclists who sometimes feel obliged to use the pavement out of fear of traffic and who show consideration to other pavement users when doing so. Chief police officers, who are responsible for enforcement, acknowledge that many cyclists, particularly children and young people, are afraid to cycle on the road, sensitivity and careful use of police discretion is required.”
Furthermore, bells not required by law:
At the point of sale (ie shops) bikes have to be fitted with bells but there is no legal requirement for them to be fitted to bicycles no longer on shop display. [NOTE: thanks to the Coalition Government's Red Tape Challenge this requirement will be history soon but, for now, is still in force).
The Highway Code does not stipulate that bells must be used. It states: "Be considerate of other road users, particularly blind and partially sighted pedestrians. Let them know you are there when necessary, for example by ringing your bell."
Another 'audible warning device' is the human voice: a polite 'excuse me' can often come across as a lot less aggressive than the apparently insistent tinkling of a bell. However, 'angry of Tunbridge Wells' type letters to newspapers continue to insist that cyclists - from church-hopping old maids to downhill mountain-bikers - ought to use bells, despite the fact their use often scares the bejesus out of pedestrians.