For London: Stop The War Coalition, CND and the Muslin Association of Great Britain has called for a massive "Troops Home" demonstration on Saturday March 19th - 1pm
See also http://www.internationalanswer.org
For Glasgow: Troops out of Iraq March and rally
Assemble South Hanover Street (off George Square), 11.30am. March to rally in St Enoch Square at 12.30 pm.
Called by Scottish Coalition for Justice Not War and Justice for Gordon Gentle Campaign
March 19th is also the day chosen by the Assembly of the Social Movements at the European Social Forum in London for a European wide mobilisation, just prior to the European Council meeting in Brussels. So expect large protests around Europe and focussed in Brussels, with a much wider set of social justice anti-neoliberalism themes than just anti-war.
See: March 19: European Actionday in Brussels - Call Out