In reply to TobyA: Not sure where in the UK you live. In Scotland it is (or was when I worked in transport industry) a statutory requirement to provide school transport when a pupil lives 3 miles or more from the zoned school. Local authorities can opt to provide a more generous policy if they wish, and they often do. For example, kids can often get transport if they live nearer to the school, as long as there is a space free on the bus, also some councils provide transport in the winter months for kids living closer to the school than three miles. In addition to this, if you can demonstrate that if your child has to walk along a dangerous route to school, they might get a discretionary entitlement to transport.
Find out what your local council's criteria are, then go from there.