Her Majesty's secret service in Westminster Abbey Details of the gathering have been disclosed by the Dean of Westminster, Dr John Hall, in an interview discussing the Abbey's role at the centre of national life. He also spoke of how the Duke and Duchess of Cambridge evaded the press a few weeks before their wedding to join the full Abbey choir as they rehearsed, to finalise their choice of music for the ceremony. And he outlined the bizarre moment the President of Chile, Sebastian Piñera, turned up at the Abbey one Sunday weeks after the rescue of the 33 trapped miners - only to be sent off to wait at a local branch of Starbucks. He said the Abbey, overlooking Parliament Square, was a powerful symbol of "faith at the heart of the nation." It stands, he said, as a reminder of how Christianity is "embedded in our national consciousness." But, in addition to the great state occasions, his role has shown him an unexpected side of church and state. In 2009, as the intelligence services prepared to mark their centenary, Dr Hall was approached about the possibility of holding an event commemorate their work. "You could say it emerged out of the shadows," he said. I offered them a great service, we would have filled the Abbey with 2,000 people - they thought that might not be appropriate. In the end they agreed on a low-key plaque dedication in the south cloister attended by the Queen. "It was a very remarkable event, an amazing privilege to be part of it," he said. The Queen and the Duke of Edinburgh came, the Prime Minister, the Foreign Secretary and the Home Secretary, half the choir were there singing and the canons and me plus 54 spooks - 18 from each of the three services. I've no idea who they were except obviously that the senior figures were there and they came from every level within the organisations. The congregation sang the national anthem as the Queen entered, Gordon Brown gave a short address and the choir sang before the dedication of a plaque honouring British intelligence work. "That it was happening was a secret and obviously we closed the cloister to visitors at the time, they didn't need to know why the cloister was closed," he said. We had a lot of security people around of course but the Abbey itself was open. Afterwards they attended a reception in a side room during which the royal couple and politicians mingled with the intelligence officers. "John Scarlett who was "C" [the head of MI6] at the time said afterwards that a number of his colleagues were very impressed by the "breadth" of the Queen's knowledge of their work," he added. Dr Hall has recently published a book about some of the historic events which he has taken part in as Dean including the Royal Wedding and the visit of Pope Benedict. Among the most unexpected brushes with the limelight came in 2010 shortly after the rescue of the 33 trapped Chilean miners made headlines around the world. During a Sunday service he received word that the President of Chile had called at the West Door accompanied by a television crew and an entourage to pay their respects at the grave of Lord Cochrane, one of the founders of the country's navy. "The marshal said "no you can't come in you can't see it now because there is a service going on, go away and come back in half an hour and the Dean will receive you,"" he explained. So they went back down Victoria Street and went to Starbucks, had coffee and then came back. Last year, in the run-up to the Royal Wedding, staff at the Abbey were sworn to strict secrecy to prevent details of the plans leaking out. But despite efforts by journalists to hunt for snippets of news - even posing as tourists to engage staff in conversation - one key plank of the planning passed unnoticed. About 8pm one evening a fortnight before the wedding, the couple were ushered in a side entrance to watch a full choir rehearsal featuring most of the music for the ceremony. "It was a chance for them to hear the choir practising and to confirm in their own minds the rightness of the choices," he said. They thanked the choir afterwards. And they had to keep quiet about it of course, it wasn't just one or two of us who knew about what was being planned it was a significant element of the Abbey community. We had actually discussed with everyone the implications in terms of confidentiality and I was enormously grateful and impressed by the fact that everyone respected that. The choir also proved a major diplomatic asset in 2010 when the Pope visited and prayed at the shrine of Edward the Confessor with the archbishop of Canterbury. As he left the service, the Pope turned to Dr Hall and told him he would "very much like" him to send him some CDs of the choir. They have since been invited to Rome to perform with the Sistine Chapel choir. One of the most alarming moments came shortly after Dr Hall first joined the Abbey, when a protester breached security to interrupt a service to commemorate the abolition of slavery. The man was led away but not before he had come within feet of the Queen and Prime Minister. "I did notice that the Queen was looking on with interest," said Dr Hall. "I later got a message that the Queen had "seen worse."" : Dr Hall's book, Queen Elizabeth II and Her Church: Royal Service at Westminster Abbey, is published by Bloomsbury.