Here inside the great Westminster Hall where the Catholic martyr Thomas More was tried and executed, to the sound of Ticheli's Amazing Grace, the great and the good is slowly gathering for the Papal address on this unprecedented State visit.

With a paradoxically heavy presence, armed police are circling Parliament as Westminster readies itself for the supposed vicar to the Prince of Peace. Inside, Roman Catholic and other MPs, along with a number of other notables, are mingling in keen anticipation. Ann Widdecombe sits smilingly next to Ruth Kelly, as party divides are forgotten. A number of senior politicians and recognisable faces -- including Jeffrey Archer -- are here before hundreds here before the living former prime ministers Gordon Brown, Tony Blair, John Major and Margaret Thatcher.

But despite the light atmosphere, the Pope faces a huge challenge this afternoon when he speaks at 17.00hrs after being introduced by the Speaker, John Bercow. He has had a hugely successful trip so far, with thousands turning out in Scotland, iconic images of baby-kissing and a lively inter-faith event at Twickenham this morning, none of which has been disrupted by the alleged terror threat foiled this morning. As we wait, the Pope is set to meet the Archbishop of Canterbury, Rowan Williams, who is right now issuing an important statement on the visit. But he so far only nodded to the child abuse scandal threatening to overshadow the trip, talking this morning of the need for Catholic schools and institutions to protect the young. Observers expect Pope Benedict XVI to reiterate his strong message about "aggressive secularism". But some hope he will go further to apologise for the negligent approach taken by the church hierarchy -- this Pope arguably included -- over abuse.

Watch this space.