LONDON:
Thousands of people marched through central London on Saturday April 12th for the Stop The War coalition's national demonstration. As two marches joined at Parliament Square (pics), a minutes silence was observed in memory of the dead in Iraq as flowers were laid in rememberance (pics). Hundreds more flowers were also laid opposite Downing Street to shouts of "Blair Out!" (pics).

Organisers estimated up to 200,000 people attended, while the police maintained only 20,000 people took part in the rally in Hyde Park (many observers said it was closer to 100,000). There were three arrests in the park, one for alleged assault on a police officer as police harrassed people at an information stall, eye witness reports tell a different story however (read report and pics here). There were speeches from dozens of speakers (streamed and archived here) throughout the afternoon.
London timeline + tactics discussion
General pictures, Samba pics, Stop the War Coalition pics.

GLASGOW:
2000 people marched through the city centre of Glasgow in protest of the war in Iraq and for justice. Police presence was small and the atmosphere was sombre and quite restrained. Speeches were made by the various political parties.
Glasgow report