The UK terror threat level has been lowered from \"severe\" to \"substantial\", the Home Office has said, according to a report on news.bbc.co.uk.



The level was raised in 2007, meaning a terrorist attack was \"highly likely\". The downgrading means there is a \"strong possibility\" of an attack.



Home Secretary Alan Johnson said there remained a \"real and serious threat\" from terrorists and the public would see little change in security measures.



The level is set by the UK\'s Joint Terrorism Analysis Centre (JTAC).



The JTAC, which is a unit within the security service MI5, sets the level based on the intelligence available about terrorist intentions and capabilities.



According to BBC home affairs correspondent Danny Shaw, security sources said the decision to change the threat level was a \"finely-balanced judgement\".



The sources said the level was \"under constant review\" and could go up again if it was felt appropriate, our correspondent added.



The JTAC states that the current threat to the UK \"comes principally from al-Qaeda and related networks\", but \"Northern Ireland related terrorism (is) also still a threat\".



At \"substantial\", the threat from terrorism is at its lowest since levels were first made public three years ago.