A couple of errors here. Firstly, the LEA does not use AA's Routemaster:
We use a database that combines the
Ordnance Survey ‘Integrated Transport Network’
(ITN) data as at 17 November 2006 plus a database
of footpaths, entered on our system before 17
November 2006, which have a proper made-up
surface such as tarmac or concrete.
Also, you can contact the LEA to ask them to accept a route which you feel they have not taken into account:
If you think that
your child’s ‘shortest appropriate route’ may include
footpaths or roads which may not already be
included in our database, please check this with us
before 17 November 2006.
(Both from the current LEA Admissions guidance).
As ever, a quick call to the LEA would establish this info. I really really recommend that people check things such as this with the authority. This forum has invaluable advice, but it is not infallible.