Sorry, my point wasn't clear--I meant that in order for TfL to 'just take a street over', i.e. without the safeguards in the GLA Act, that would require primary legislation, to establish some kind of unilateral power. I lost the point because I started going on about something else.
They literally can, but it requires the consent of either borough or the Secretary of State. See section 5:
https://www.legislation.gov.uk/ukpga/1999/29/section/261
I can’t see them siding with the Mayor over K&C, even if the bike lane policy and cash comes from central government.
(I’m as puzzled how the lane ever came into existence given what we know about K&C)