Update 13:40 - Police have now confirmed that a non-specific threat has been made by Irish republican dissidents. Sky News has further comment.
Update 13:20 - It should be pointed out that the 'IRA' disbanded in the 1990s, and the rumoured involvement of an Irish group would be from a separate republican group.
Update 12:30 - Sky News just tweeted that their 'sources' suggest a coded warning from Irish Republican dissidents of a bomb in central London. Are Sky's sources better than Twitter? Who can say?
Unverified rumours are circulating that
the IRA an Irish republican group have issued a bomb threat to London, while several roads in the capital were earlier closed by police.
A 'disturbed manhole cover' sparked the cordon in the Trafalgar Square area this morning, with roads including the Mall, Carlton House Terrace and Northumberland Avenue affected. Meanwhile, a suspect bag was destroyed by controlled explosion. Blottr has purported images of the incident.
Links to Irish republicans currently remain in the realm of Twitter gossip, but we'll keep an eye on the story and update this post with any developments.