Well, you need to get that impression out of your head pronto, because there is no such allowance, other than claiming "de minimis" at the adjudicators, who may well not agree with you. In fact some adjudicator don't recognise "de minimis" at all.
For so many years I've been assuming there's a little leeway.. See here, specifically 1.15:
Eops Schedule 2 (SoR) Appendix 9 TfL Business Ruleshttps://content.tfl.gov.uk/eops-schedule2-appendix9-tfl-business-rules.pdf"A representation is made on the basis that the driver had to temporarily drive in a bus lane, in order that they could turn left to access a side road or driveway."
"if distance within the Bus Lane is less than 20 metres, accept."
A look at GSV compared to the photos shows you were in the bus lane for about 40 metres, way over any possible "de minimis" argument, sorry to have to say it. So the contravention is made out, I'm afraid.
Thanks for your honesty, although wouldn't say 40 metres, if I remember correctly about 4 cars. Getting a fine because all the vehicles in front of you want to go ahead and you want to turn left thus keep the traffic flowing.. This is going to make me question the next time I go into a bus lane only to move around a vehicle when they're turning into a side road. I've seen people do this and it's quite woeful.
However, this may not be game over, because experts on here have found many "technical" appeal arguments based on poor management by the council, (or TfL), of the enforcement process, so wait a bit for more contributions.
Anyway I can confirm or check if this is the case? Also would the lack of a blue sign near the middle be a case to go on as it is a bit long, because mistakenly as it was dark part of me at the time thought it was way passed the usual time a bus lane is operational.
I also turned from Webber Row (opposite side) so many things to look for when turning and that sign I did not see. I've been at this road before and wondered why there wasn't a sign.
See - Case 5 – Inadequate signage
Adjudicators decisions and case studies for a bus lane PCN
https://penaltychargenotice.co.uk/bus-lanes/adjudicators-decisions-and-case-studies-bus-lanes/The post
here seems like a sign existed before.