The first thing that comes to mind is that the location given on the PCN is not specific enough. However, you've told us you drive along this road, (and beside the bus lane) four times a day, so would be reasonably aware where the alleged contravention took place.
So as you are familiar with the location, please post up a GSV link to the bus lane concerned.
As well as the contravention, there have been serious issues with TfL management of the enforcement process such that appeals have been won on that basis, rather than refuting the alleged contravention
So wait a bit until those expert in these matters respond. As for your reason for entering the bus lane, this is mitigation, so could not be considered at London Tribunals.
