A House of Commons spokesman said: ‘We have contingency plans to cover a range of emergencies, of which this [an armed raid] is one. It does not relate to a specific threat.’In other words, not really a news story at all, just a typical bit of Daily Mail tub thump to encourage us to feel scared and suspicious.
1 - "Westminster on Mumbai-style terror attack alert after Al Qaeda threat," by Gerri Peev. Published in the Daily Mail, 16th of November, 2010. (http://www.dailymail.co.uk/news/article-1330066/Westminster-Mumbai-style-terror-attack-alert-Al-Qaeda-threat.html#ixzz15TVIJ1hP)