The remit of the Arts Council Collection, which started in 1946, is to collect contemporary British art and promote it throughout the UK. It has now built up a collection of 7,500 paintings, drawings, sculptures, installations, videos, films and photographs.
A 'collection without walls', the work is loaned to museums, galleries and other public spaces and also used to create travelling exhibitions that are run through the Hayward Gallery's touring arm, known as National Touring Exhibitions.
The next one is Size Matters, which is launched this month and examines the way artists use the power of scale to distort perceptions of reality.
But what makes the collection really unusual is the emphasis on continued acquisition, and though a budget of £150,000 may be a lot in museum terms, in the world of modern art it is small change.
This means that May, along with five others on the selection panel she chairs, has the difficult job of trying to buy work by artists established enough to be considered significant, but before the prices have gone skyward.
It is the art equivalent of putting all your money into promising internet start-ups and banking on every one of them turning into Lastminute.com.
May admits that collecting is risky: 'You're looking out for artists who are making work of quality and whose practices are developing, and there is the added difficulty of getting things too early, because they could move to a different level and you want to get work which is really representative.
But that's what is exciting, because it is a gamble. And unlike a private collector, you can't sell.'
The collection is based for administrative purposes at the Hayward Gallery, part of the South Bank Centre in London, and May's office is nearby in the Royal Festival Hall, which is where we meet.
We are on one of the hall's balcony floors, ostensibly to escape the noise from the open-plan office, but we reckoned without the class of school kids in their maroon uniforms having lunch. Above the chatter, May enthuses about the collection, taking me through a slide show on a laptop of some of its most important pieces, reeling off names of the great, the good and the controversial.
Much of the work in the collection is the kind of thing the Daily Mail loves to hate, but the cutting edge is where May is comfortable, where artist and observer are so attuned that the tiniest of gestures can change the whole tenor of a piece. The flip side with such radical work is that it is inevitable that the selection panel makes mistakes, a fact she's happy to acknowledge.
'There are things that sit very oddly in the collection, though I'm not going to give an example,' she says. 'But our collection is a snapshot of what's going on in British Art; the good and the bad.'
She also refuses to name her favourites, saying it could be any one of 100 works, but that she is 'like a mother with her children', when it comes to the collection.
But it is clear from the slides that the collection panels have been highly successful over the years, from getting one of Francis Bacon's series of 'screaming Popes' for a few hundred pounds, through to work by David Hockney and up to today's Turner Prize checklist such as Damien Hirst, Gary Hume and Tracey Emin.
This list was bolstered by the generosity of Charles Saatchi - or his rivalry with Nicholas Serota and the Tate Modern, depending on your viewpoint - who donated 134 works in 1999 and 2003, estimated to be worth £750,000.
Surprisingly, given the dominance of conceptual art in recent times, May herself was a figurative painter before becoming a curator. Born in Manchester in 1968 to working class parents, her father was a painter and decorator and her mother ran a shop.
She was good at many subjects at school but was set on art from early on. Despite the fact that art was seen as a risky profession by her teachers and school friends, after O-levels she did an art foundation and then went to the Liverpool School of Art.
Once she graduated, May moved to London in the early 1990s to try and make it as an artist. She rented a freezing studio in the East End where she would occasionally see other artists such as Rachel Whiteread wandering past her window.
To support herself she worked part time at the Hayward Gallery as an assistant exhibition organiser. Eventually she gave up painting to become a full-time curator.
She hasn't picked up a paintbrush for ten years now, but says she has no regrets: 'It was absolutely the right thing to do. When you work on a piece of art you are putting so much of yourself into it and so when you reveal it to the wider world you are exposing yourself to scrutiny, and I wasn't robust enough to do it.'
She became the exhibitions curator at the Hayward Gallery in 1994, and five years later moved downriver to be a curator at the Tate Modern. One of the many shows she curated was Olafur Eliasson's The Weather Project in the Tate Modern's Turbine Hall.
She left the Tate in August last year to take up her present post, but says she departed on a high, having set up the Untitled series of exhibitions, which showcase contemporary art. The opening show featured a gallery that was empty apart from a small box with a replica sparrow apparently suffocating.
She says the exhibition was an exhilarating but also bruising experience. When it opened a journalist asked her if she thought children would like it, and when she said she hoped so, he quoted her saying it was 'particularly suitable for children', and the letters of complaint started to pour in. 'It was fine,' she says, 'I just put it down to experience. It toughened me up, I suppose.'
Tate Modern may be one of the most successful modern art galleries in the world, but the chance to be uncovering the future of British art was too much to pass up, so when Isobel Johnstone, the former head of the Arts Council Collection retired, she applied for the job.
'I've always thought this is one of the best jobs in the British art world. The collection is growing and it has a designated acquisition budget, so there's great scope. It is well loved and supported by artists, and I wanted to work with that and maintain that support.'
Though the collection doesn't have an exhibition area at the Hayward, it recently got its first dedicated space when the sculpture moved to the Longside Gallery at the Yorkshire Sculpture Park.
The new location allows for better storage and the collection shares an exhibition space in the gallery. She has also just finalised the lease for a new store in south London for the two-dimensional collection and it is scheduled to move in at the end of 2005.
The new store will allow for a better photography programme - a recent feasibility study has looked at digitising the whole collection - and more systematic conservation. It will also have a viewing room to make it is easier for borrowers to see works before they take them.
Next year is the collection's 60th anniversary, and to coincide with this, May is working on a new programme called Select, which will encourage museums and galleries to create exhibitions using the collection. The collection's curatorial team will offer expert advice where needed.
The project is part of May's mission to raise the collection's profile. She says she doesn't see the Tate as a rival, but her time there has obviously taught her about the power of being in the public eye.
'At the moment we suffer from a degree of invisibility and the way of dealing with that is to get as many works out in the country as possible,' she says. 'I want to make the collection a household name.'