There has been a lot of discussion in the past about the discounting of fares and having to charge the amount displayed on the meter? Probably the most informative case on this subject is the one brought by Mr Kelly of Merseyside in 1993 on behalf of his company, Curzon ltd.
Anyone who has any doubts as to how the law stands on this particular subject should read this case. It should also be remembered that if a byelaw is incompatible with statute legislation (which many are) then the statute legislation takes precedent. In many cases the existance of a byelaws does not necessarily mean they are lawfull?
http://taxi-driver.co.uk/phpBB2/viewtopic.php?t=3623
Regards
JD