So, from your narrative, you were in traffic driving along, wanting to park, saw a parking space available just before the bus stop, so stopped by the bus stop momentarily, then reversed into the bay, correct ?
If so, then there really is no contravention, and I think a similar case was won last year on this, (it may have been more than one year). Trouble is I don't know where in London it was so can't post the case number. Hopefully somebody on here will remember. Of course if you waited whilst a car departed and left the space for you, then it is not so clear-cut.