British backing for African forces tackling Islamist insurgents will be doubled today as more than 50 countries head to London to discuss ways of stabilising the country.

David Cameron will open the conference with a warning that the turbulence in the failed state threatens the security both of Africa and of Western nations.

The summit, which will be attended by the United Nations Secretary General Ban Ki-moon and the US Secretary of State Hillary Clinton, will aim to build on the tentative political progress in Somalia.

The UN has agreed a boost to numbers of African Union soldiers in the country and Mr Cameron will announce that funding for its military presence is to increase from £5m to £13m. The cash would be used for logistical support.

British sources confirmed Britain and other EU nations had examined the feasibility of air strikes against fighters from al-Shabaab, as well as the pirates operating off the coast.

However, they played down the prospect of any imminent action, insisting they wanted AU forces to take the lead in any conflict.