The Royal United Services Institute in the United Kingdom just released a report titled UK Terrorism Analysis that looks at the threat to the 2012 Summer Olympics in the UK.
It covers a variety of terrorist threats, including the possibility of "lone wolfs" coming from conflict zones in Somalia, Nigeria and Yemen. The report indicates that Britons are thought to make up 25 percent of the 200 or so foreign fighters currently with al-Shabaab in Somalia.