The threat of an Al-Qaeda attack on Britain is lower than at any time since before the 9/11 attacks, MI5 has privately concluded. Well-placed officials said there had been discussions in MI5 over the past month about whether to reduce the terrorist threat level from severe where an attack is deemed highly likely to substantial, where it is a strong possibility. The assessment follows Operation Pathway, one of MI5s biggest counterterrorist campaigns. It led to the arrest of 11 Pakistani men in April. The men were released without charge. When no explosives or weapons were found, critics said the operation revealed the absence of any terrorist plot against the UK. Although MI5 declined to comment, evidence of the perceived lower risk came last week when the US navy moored a warship, the Halyburton, in London. The Americans wouldnt dream of [it] if the threat of an attack was high, a security official said.