A low-key protest by online activists has started outside the UK Government Communications Headquarters (GCHQ). http://www.bbc.com/news/uk-28979524
A larger demonstration by the We Are Anonymous group is expected over the weekend although there is a large police presence at the Cheltenham site.
Protesters are supporting a legal challenge by civil liberty groups against the alleged use of mass surveillance by intelligence services.
The UK government says interception is subject to strict controls.
Gloucestershire police said the number of protestors at the scene were outnumbered by officers and members of the media.
Officers from forces in Kent, South Wales and the Metropolitan Police had all been drafted in.
The BBC was told that staff were driven on to the site by bus on Friday morning. Normally, they are dropped off outside the complex.
Earlier reports suggested the protest could have been delayed due to the low turnout.
Privacy International and Liberty are among those challenging the legality of alleged “interception, collection and use of communications” by agencies, at the tribunal.
This follows revelations by the former US intelligence analyst Edward Snowden about UK and US surveillance practices.
The case – also brought by Amnesty International, the American Civil Liberties Union and other groups – centres on the alleged use by UK intelligence and security agencies of a mass surveillance operation called Tempora.
The UK government has neither confirmed nor denied the existence of the operation.