Campaign Against Arms Trade is seeking judicial review of the UK government's failure to revoke any licences for arms exports to repressive Saudi Arabia.
Multinational arms firm BAE Systems were forced to abandon attempts to run a workshop at the University of Manchester last week amidst a series of protests.
Campaigners will attned the Spirit of Summer Fair in London this weekend to highlight the fact that the owners, Clarion Events, are also involved in the arms trade.
The chairman of BAE Systems has said he is happy to continue selling arms to Saudi Arabia, although they have been used to suppress peaceful protests in Bahrain.
The Foreign and Commonwealth Office's Strategic Export Control Reports reveal the UK government continued to licence arms exports to Libya till the end of 2010.
A demonstration outside the Treasury has called for cuts in military spending, including subsidies for the arms trade, at a time when other areas face severe cutbacks.