Simon Buchanan is defiantly cheerful when we speak, just days ahead of the opening of the 40th and last ever Art In Action at Waterperry.

The pivotal and ground breaking national art show is not only unique in that it gathers together’s the country’s finest artists by genre and then allows the public to watch them in action, but also that it is a charity (The Waterperry Estate is owned by the School of Economic Science, a centre for spiritual and practical knowledge and enquiry) – whose volunteers are on their knees it would seem.

Surprisingly then, Art In Action is as popular as ever – 25,000 guests are expected to pour through the gates in the next four days to witness the 400 artists on show, but has become unmanageable.

None of which Simon was prepared for when hetook over Art In Action’s reins from founder Bernard Saunders. As steward of the Waterperry Estate he was full of brilliant ideas on how to modernise the Oxfordshire art show, and make it more efficient, not finish it off all together.

“I have lost a lot of sleep over it I must admit,” Simon admits, “lying awake at 2am staring at the ceiling and wondering if we’ve done the right thing. Many of the artists are furious because is was very lucrative for them. But the volunteers who run it are the same ones who have been doing it for 40 years and they are octogenarians now and exhausted.

“Quite a few volunteers had to pull out because they have angina or illnesses. Many are in their 80s, and we've tried to get new blood in, but they want paying because it takes a whole year to plan Art In Action and they don’t want to do that for free.

There are very few youngsters coming through the ranks willing to clean the toilets or lug heavy sets and machinery around for free.

“I remember when founder Bernard Saunders said I would have to wind up the show and I was horrified, but the writing was on the wall and it's is the right time. I will just have to wear a bulletproof vest for the artist's dinner," he adds sadly.

Of course the other option is to start charging the artists, to make it a more commercial venture, but Simon says it would mean Art In Action would lose its essential ethos and vibe – one of benevolent calm and creativity. “What people like so much is the spirit of selflessness. It is unique, and making it more commercial would change it fundamentally."

Simon is considering different formats, including several festivals that run throughout the year rather than one bonanza, but for the moment we face the last Art In Action ever.

It will however be the best, as Simon and his team have been beavering away behind the scenes to make it more accessible and contemporary. This year there is a Zen tent with Japanese tea and calligraphy by the river and even a swordmaster, sculpture has been moved into the walled garden, there are more performers and theatre shows, a digital art tent full of computer games, graphics and preview modelling, hosted by Chris Antonio from one of the big gaming houses in Soho, a packed glass blowing tent, Flamenco dancing, famous musicians, Odissi dancers, surfboard makers in the woodwork tent, installations all over the site, a kids climbing frame, and even a pancake kitchen, plus The Great Pottrery throw crew will be there from the BBC.

And the practical classes, which are always the creme de la creme are inspirational. You really can go and watch a master craftsman or artist at work and then book into a class and get taught how to do it yourself.

So how does Simon feel on the eve of the final bow? "We have supported the arts for 40 years, financially sometimes we didn’t even break even and in 2012 when we had disasterous weather we lost £80,000 so we have given a lot and been more than generous.

"And we need to look at that and see Art In Action as a massive success. We should be celebrating and go out with a bang. Besides Waterperry has so much potential,” Simon adds, “so let’s just see what happens. It would be great if it could turn into an arts and horticultural centre but in the meantime let's have massive artistic knees up.”