The House of Lords ruled yesterday that the detention of thousands of people for several hours at Oxford Circus on 1st May 2001 was not a breach of any rights.
tl;dr: "Anyone on the streets must be taken to be consenting to the possibility of being confined by the police."
The full judgment:
http://www.publications.parliament.uk/pa/ld200809/ldjudgmt/jd090128/austin-1.htm
See here for the earlier judgments:
http://www.bailii.org/ew/cases/EWCA/Civ/2007/989.html
http://www.bailii.org/ew/cases/EWHC/QB/2005/480.html
Where abouts is that bit about consenting to the possibilty of being confiend by the police, i tried doing a text search but could not find it in the ruling.