When rock stars and barristers cross paths we can usually assume drugs, guns or missing millions are involved.

But the friendship between Jon Lord and Sir John Mortimer has been forged in altogether happier circumstance, resulting in one of show business's more intriguing stage partnerships.

Jon Lord was the former keyboard player in Deep Purple, the fabulously successful heavy metal band and once undisputed holders of the World's Loudest Band title.

But, in recent months, Jon, for so long associated with such mean and moody figures as Richie Blackmore and Ian Gillan, has been happily supporting an altogether different kind of front man, in the shape of an 83-year-old raconteur and author.

Sir John Mortimer, the creator of Rumpole who lives in Turville Heath, invited Jon to join the select team performing Mortimer's Miscellany, after the pair struck up a close friendship 15 years ago, when they both became involved in the high profile campaign to save the Henley's Regal Theatre.

Jon lives just down the road in Fawley and the two men, both proud of their impressive grounds, now share the same gardener.

Oxfordshire audiences had the chance to catch them in action at a fundraising event for SSNAP (Support for Sick Newborns and their Parents) held at the Amey Theatre, Abingdon School, Abingdon, in April.

On these evenings, Sir John, knighted for his services to the arts in 1998, takes centre stage in his wheelchair usually flanked by two of his favourite actresses Joanna David and Rohan McCullough and reads poetry and tells stories from his time as a practising barrister and playwright.

Dressed in black, with his now silver hair now in a pony tail, the ex-Deep Purple man sits at the piano, providing gentle accompaniment, laughing at anecdotes he has now heard dozens of times.

"I am a huge fan of Sir John's as well as being a friend. He is a wonderful man. I love sitting at the piano listening to all the stories," Jon told me as he sipped mineral water at a post-show drinks party, surrounded by fans and supporters of SSNAP.

Things had certainly changed since I last saw Jon, at a performance on Purple's Burn Tour in Preston. If gigging never used to be like during his days with Deep Purple and later Whitesnake, neither were the parties we can safely assume.

But, in a way, Jon, who only finished playing in the reformed Deep Purple in 2002, was always something of a refined rocker, as at ease with prominent conductors as preening leather clad vocalists like David Coverdale.

Slightly older than the other members of the band, one foot was always firmly planted in the classical camp and bringing different world together has always been something of a Lord speciality.

In the late sixties he famously created the Concerto for Group and Orchestra, the first serious attempt to marry rock and classical music.

Many others, from Emerson, Lake and Palmer to Elvis Costello, have followed a similar path, though none with greater ambition or self confidence. On July 7 Jon will be performing his most famous piece with the Bournemouth Symphony Orchestra at what is certain to be one of the highlights of this year's Henley Festival.

"I've always loved all kinds of music," said Jon."When I was five my dad noticed I could pick out a tune on the piano and so arranged for me to have piano lessons and my classical training went from there.

"When rock n' roll appeared on the scene I immediately fell for it, but I didn't lose my love of classical music. To this day I don't compartmentalise if it speaks to me I enjoy it."

Soon after Deep Purple was formed, he heard an album by the Dave Brubeck Quartet with the New York Philhamonic Orchestra, music written specifically for jazz band and orchestra. It inspired him to reach for a copy of Forsythe on Orchestration, and getting to work on his famous crossover' concerto.

It was performed at the Albert Hall by the Royal Philharmonic, under Sir Malcolm Arnold, alongside Deep Purple in 1969 and apart from special 30th anniversary shows, has rarely been performed since.

When he was invited by Henley Festival's artistic director, Stewart Collins, to revive the piece for a one-off UK performance, Jon was delighted.

"It seemed so fitting the year I turn 65. Henley and the surrounding area is very much my home and I really want to be part of a festival that I have seen grow and grow over the years. I have been coming as a punter now for a long time and I have always wanted the opportunity to perform on that Floating Stage there is nowhere like it in the world."

It will be performed by the Bournemouth Symphony Orchestra, who we may assume will show greater respect than the first classical musicians to be presented with the piece.

"They couldn't take it seriously at first and wolfwhistled when we first met them," Jon recalled. "But Sir Malcolm Arnold, the conductor, was a wonderful ambassador and a great supporter of my work and told them all after a slightly scrappy dress rehearsal: We are going to make history tonight. We might as well make music at the same time. I'll never forget the way in which everyone pulled together to produce a wonderful performance.

"I had been very aware of the differences between the non-amplified instruments of the orchestra and the amplified band. Both are worlds apart. I had to write music that celebrated the differences but that also brought the two together in peace and harmony. I am very aware that very often bands use classical music purely as a backing. But this isn't what the Concerto is about."

The piece includes vocals in the second movement, apparently written on the afternoon of the first performance by Deep Purple's front man Ian Gillan.

"The rest of the band had initially been quizzical to say the least. They did not read music and I had to teach them by rota. But the vocals are beautiful," said Jon, "written by a man feeling quite intimidated at being faced with a packed Albert Hall, a slightly worried RPO and a larger than life conductor."

This time it will be different. "This performance will be more Henley on a summer's evening than Wembley Arena. It will be more gentle and there will be less volume, to suit the setting. I am inordinately proud of the piece. It is my baby."

Jon moved to Henley in the 1970s, and like George Harrison before him, fell in love with the Thames-side town.

"I have travelled thousands of miles and played on countless stages, But I have always thought this the most beautiful place in the world."

One of his two daughters, Amy, who went to Gillotts School, now works in the town as the events manager at the Hotel Du Vin. His other daughter Sara works in the music industry.

Jon is now busily writing music and has set up a new 12-piece group, called the Gemini Band, which will embark on a world tour from November. A piano concerto is being recorded by EMI Classics and a Choral piece, From Darkness to Light, is to be performed in Hereford Cathedral.

Next year there are plans for a new orchestral piece in Durham Cathedral to mark the 175th anniversary of the founding of Durham University.

Hopefully, the shows with Sir John, usually performed for charity, will also continue. Sir John, who has holidayed at the Lords' holiday home in Minorca, is dedicating the next Rumpole novel, Rumpole and the Reign of Terror, to his cultured Henley friend. The more you think about it the literary knight and Lord of the keyboard are really not such an odd couple at all.

The 2006 Henley Festival runs from July 5 to 9. Tickets are sold per evening, giving festival-goers a range of top-class entertainment on each and every night. As well as The Rock Orchestra on Friday, July 7, treats in-store include Welsh baritone Bryn Terfel, a musical evening inspired by Shakespeare with Zo Wanamaker and Robert Lindsay, a celebration of the music of Leonard Bernstein, Status Quo as part of their 40th anniversary tour and much more in the way of music, street theatre, comedy and visual art.

For more information visit the website at www.henley-festival.co.uk For tickets contact the Box Office on 01491 843404, boxoffice@henley-festival.co.uk