Twickenham Council have decided in their wisdom that I've driven too far in a bus lane.

They want to fine me £100.00
Yes I entered the bus lane, but their own cameras show that
within 30 seconds my car was parked in a designated bay which was only accessible by going through the bus lane.
From the photos the council have provided I have driven no more than 6 car lengths from the point that the car tyre first crossed into the bus lane, to the point of the bay that I used. There were no busses to be seen, whilst the traffic lane was at a vitual standstill.
I'm looking for specific information for a robust defence. The specific issues based on the councils' own reply is "vehcles ... are only permitted to enter the bus lane
near to the intended location (parking bay) in whcih the motorist proposed to use. I've highlighted what appears to me to be the critical word.
There are two specific questions:
a) What legislation is used to define and thus enforce bus lanes
b) What is the definition of "near", in a legal sense as far as bus lanes go.
I've done an initial

but can't find anything other than how to appeal.
Thanks in advance.