It's been four years since the American evangelist Billy Graham died, and it's still difficult today to imagine the world without him. Apart from the successes of his worldwide evangelistic crusades, we know that in the corridor of the most powerful country in the world, he was the quiet voice, offering spiritual guidance to every American president, from Harry S Truman to Barack Obama.

Graham came to Britain in March 1954 for a series of evangelistic crusades at the Haringey Arena in North London. There was quite a bit of fuss in the churches in England and also in the press about the visit, but Graham made it clear in his first sermon, why he came:

"We've not come here to the city of London to save England. We have not come here with any great ideas that we will tell you how to do it. We haven't come here to try to reform you. We have come here ... to help lead you in a crusade to win men to Jesus Christ and help promote the kingdom of God in Britain."

The original idea was for Graham to stay for only one week, but the demand to hear him speak was so great that he ended up staying for three months.

For twelve weeks, 12,000 people filled the Haringey Arena every night, and even on the last day, the demand was so great to hear Billy Graham, that the organisers decided to move the service from Harringay to Wembley Stadium to accommodate the 120,000 people who wanted to hear him.

Even that wasn't enough, and the organisers again arranged another service, this time, at the White City Stadium in West London for 65,000 people who couldn't get into Wembley.

Haringey was an enormous success and the number of people who attended is staggering. Over two million people went, with over 40,000 committing their lives to Christ. A year later, Graham came again to London for a week-long crusade. It rained every night except for the final night which also turned out to be the coldest night of the year, but that didn't prevent 450,000 people from turning up, with over 24,000 committing their lives to Christ.

In 1966, Graham came again to Britain for another crusade. This time he went to Earl's Court in West London. The criticism that began in the press in 1954 had by now reached fever pitch. They were saying that so many people went forward to 'accept Christ at the Crusades' because of the 'emotional intensity' of Graham's signature song, 'Just as I am,' which the choir always sang before he made his appeal.

Stung by this criticism, Graham decided to drop the song altogether and appeal without any song or music. Writing many years later, Cliff Barrows, Graham's musical director, recounted the effect.

"We went thirty nights without a single note of the hymn. 'Just as I Am' has always been our crusades' signature tune through the years. We had never done that before. When the reporters began to write about the invitation at Earl's Court, they said all they heard was a shuffling of feet on the floor. 'Bring back 'Just as I Am' as the silence is killing us!'"

Apart from the 'Just as I Am' controversy, the Earl's Court Crusade was national news for another reason. In the 1960s, Cliff Richard was a massive pop star and when he announced that he was a born-again Christian and would be at the Earl's Court Crusade, the press flocked there to cover the story.

To put this into perspective, in today's terms it would be like Ed Sheeran or another top pop star announcing that they were now a born-again Christian and would be attending a church service at the 02 Arena in London. In the 1960s, Sir Cliff was a massive star and becoming a born-again Christian was big news.

I remember it well as my father took me to Earl's Court, and after his introduction to the stage, Sir Cliff appeared wearing black-rimmed glasses, acoustic guitar in tow. At first, there was this uncanny silence as neither the press nor the 27,000 people there knew what to expect.

In a few words, Sir Cliff confirmed that he was a born-again Christian and proceeded to sing the well-known evangelical song, 'It's no secret what God can do'. When he finished, there was a dignified uproar, and he went outside and repeated the same for the thousands of fans who couldn't get into Earl's Court. The following day, 'Cliff at Billy Graham's Crusade' was headline news in all the papers.

Although a relatively small community but substantially more than in 1954, many West Indians went to Earl's Court. They enjoyed this national public display of evangelical Christianity and returned to their churches spiritually refreshed and uplifted. Crucially, they took away with them the free songbook with all the songs from the rusade, and soon they were singing the likes of 'Blessed Assurance', 'The Old Rugged Cross', 'I Am Thine Oh Lord', 'Love Lifted Me', and 'How Great Thou Art', in many of their services.

Fast forward twenty-five years, I was at the BBC, making a programme to commemorate the anniversary of Billy Graham's visit to London. We were able to get both Billy Graham and Sir Cliff as our special guests. Filming the programme, I remembered Earl's Court and asked Sir Cliff if he would sing again, 'It's no secret what God can do'. He agreed, picked up his guitar, and launched again into the great song.

When editing, I cut from this to the black and white footage of him on stage singing the same song in the same key! It was a magical moment, for I was a fan and a great admirer. Life, it seemed had come full circle for me.

Usually, when filming an interview, the producer and presenter agree on the questions and the line of questioning. The interviewee often does not know the questions. Billy Graham was ok with this and gave perhaps the best answer to many of the timeless questions we all ask. 'Why does God allow ...?' 'Where was God when...?' 'If there is a God, why did He make this happen ...?'

Billy's answer to questions like this - which he must have heard a thousand times and perhaps even contemplated himself - is perhaps the best I have ever heard:

"These are the questions I'm going to ask God when I meet Him."

There is no better answer.

Roy Francis is an award-winning former BBC 'Songs of Praise' producer and the author of 'Windrush and the Black Pentecostal Church in Britain'.