IT’S just after lunch and there are books everywhere. Around the room, small teams of people are sorting them into some kind of order but getting about the place is not easy. In front, behind, to the sides, under, and above, are books, books and books. They’re even spilling out in to the street, in boxes upon boxes, and now here’s a car pulling up at the pavement with some more. For a book lover, it’s perfect, like the Kindle was never invented.

The reason for the organised chaos is that the popular, famous, much-loved and frankly legendary Christian Aid book sale is on again in Edinburgh. The sale, which is held at Andrew’s and St George’s West Church on George Street, has been running since 1974 and has now become the biggest second-hand book sale in the world. On the first day of the event, people queue up, elbows freshly sharpened, wallets freshly stuffed, because they know they are likely to find something interesting, maybe something rare and very possibly something unique. One year, a man even turned up with a shopping trolley, ready to fill it with books, which he did.

In all, some 500 volunteers are needed by Christian Aid to keep the event going, with everyone doing a slightly different job. Out on the street is a small team led by 57-year-old Michael Thom, whose job it is to accept the donations at the door; there are also more than 30 drivers who go all over the city to collect donations.

Elsewhere, the volunteers are divided into groups, sorting the books into categories (Scottish books are the most popular and best-selling) and deciding what might be valuable and what might be less so. It’s impossible to say for sure, but there are probably around 60,000 donated books and collectables in this building, which means a lot of sorting.

In charge of all the organising and sorting at the church is Lady Mary Davidson. She started the event here in the early 70s with a couple of trestle tables and a few donated boxes of books, and more than 40 years later here she still is, the matriarch of the bibliophiles and box-humphers and a sharp, friendly presence who can point out what needs doing and hand out praise, or the odd gentle push, when necessary.

Standing in the middle of the city of books, Lady Mary tells me that the first day of the sale this year has been a huge success. Over the years, the event has raised several millions for the charity, which works to end poverty around the world, but this year has been particularly good. On the first day alone, says Lady Mary, the sale has raised £63,000, which is £18,000 more than 2017. “It’s much bigger than last year,” she says. “Of course, the weather is everything.”

It turns out this is one of the surprises of the sale – that in the age of Amazon and Kindle, it keeps on growing – but it is not the only one. Christian Aid was first founded by British and Irish churches to help refugees after the Second World War and now provides humanitarian relief in 40 countries; it also raises money at this time every year through the Christian Aid Week fundraising campaign. But the volunteers of this old, established Christian charity are not entirely what you might expect. And they’re not here for the reasons you would expect either.

Near the back of the church, where a small team is working out possible valuations, I meet 54-year-old Ried Zulager, who, remarkably, flies in every year from Washington just to volunteer at the sale, using up his holidays from work to do so. The American first became involved when he was a student in Edinburgh, studying for a PhD in Scottish history; he also worshipped at the church, and every year he presides over the special and antiquarian books, burrowing down for anything that might be particularly interesting or valuable. However, the real reason he keeps coming back isn’t raising money for Christian Aid, although that’s important, it’s seeing the friends he made here; this is a social network for which you don’t need a password.

Michael Thom, one of the team who mans the door, has a similar story. For around 15 years now, Michael has helped at the front door, lifting boxes and moving books – he also has one of the best eyes among the volunteers for spotting an interesting or potentially valuable book. He doesn’t read a lot himself, he says, but he knows a good book when he sees one.

Michael also proves an important point, which is that not all the volunteers for Christian Aid are nice retired ladies. He works hard and likes to party quite hard too; he shows me the slogan on his skip cap which reads “FRI. SAT. SUN. REPEAT” and tells me how he became involved with the sale.

“I was unemployed when I first got involved,” he says, “and I’d say it changed my life. It’s also increased my confidence coming every year and seeing friends. When I first started, they needed young men who could lift boxes so I was able to do that; now I’m starting to think that I might need some help myself.”

Mary Davidson has also been a significant figure in Michael’s life, helping him to find regular support and encouraging him to volunteer. He may have been unemployed, and his life was at a low point when he first came here, but now he works in the kitchen of a restaurant down the road, and every year he comes back to the sale for more.

“Mary has helped me a lot,” he says, “and I feel I can give something back.” This place has made him a better person, he says.

Lady Mary says this is a typical story, and says that helpers like Michael and Reid prove that Christian Aid volunteers, or any volunteers for that matter, do not necessarily fit a certain pattern or stereotype, although they do exist of course. She also believes that, even though this event has raised millions of pounds for the charity, the volunteers keep on coming because they receive more than they give.

“Books are very bonding,” she says, “and working together on them is a very good experience, with congenial people. They form great friendships over it, which continue throughout the year; there is a whole thing of coming together across these three weeks. And there are all types, from all over Scotland.”

One of them is Margaret MacPherson, another volunteer who travels some distance to get here – she lives in Glenelg in the Kyle of Lochalsh. Margaret has been coming to the sale for the last five or six years and again she confounds the expectations: Christian Aid may be a religious charity but Margaret is not religious herself, not that it matters. Michael feels the same about his faith – part of the mission of Christian Aid is to try to do as Jesus would do, but this isn’t about faith necessarily, or even doing good; amid the piles of books and groups of friends, it’s about having a good time.

Of course, it’s also about finding a good bargain. The volunteers tell me that one of their best buys this year is a copy of Ian Rankin’s first book from 1987, Knots and Crosses, signed by the author. On the day I visit, they’ve also just taken delivery of a beautiful set of magazines featuring Aly Sloper, one of the earliest comic strip characters. Part of the job of the volunteers is to work out how much they might reasonably ask for such things. Today, they think the Aly Sloper magazines might fetch at least £300.

There are many other curios on offer: piles upon piles of Victorian photographs, batches of faded pictures of soldiers from the First World War, vintage comics from the United States, bookmarks, autograph books, and on and on it goes. Last year, there was also one of the first printed board games – a little set from the 18th century called Tour of Scotland. The aim was to get round the board and the first person to arrive at No 100, Edinburgh, wins. It is extremely rare and was acquired by a private collector.

There are also paintings for sale, including a new self-portrait by this year’s patron John Byrne (it has a reserve price of £5,000). And as we wander round, we spot some other little treasures: the complete works of Sir Walter Scott, including the Waverley Novels, Poetry and Prose in a hundred beautifully bound volumes, published in 1844 (they are expected to sell for at least £1,000). And there’s a copy of The Ruined Abbeys of the Border from 1865, illustrated with six photographs by Wilson and Thompson, both Scottish pioneers of photography; using photographs as illustrations in books was, at that time, very unusual.

Lady Mary is hugely optimistic that it will all raise a large amount of money – remember, she says, that the money will support some of the poorest communities in the world. In the meantime, the work of the book sale goes on; sorting from 9am until 9pm for ten days solid, and then six days of selling. It’s hard work, and even though the volunteers love it, perhaps they’ll remember the prayer offered by the Revd Ian Gilmour, the minister of the church: let us pray for generous hearts and persistent efforts.

The Christian Aid Sale is at St Andrew’s and St George’s West Church, George Street, Edinburgh until tomorrow. For more information about Christian Aid Week, visit www.christianaid.org.uk