We were meant to be talking about what it is like working with hordes of rampaging St Trinian’s schoolgirls — well, I was, at least. But instead of focusing on how Sarah Harding had transformed herself from wild mini-skirted singer with Girls Aloud into her new role as the wild mini-skirted indie chick Roxy, the bursar of St Trinian’s seemed intent on learning more about the head of an altogether different girls’ school in Oxford.

The actor Toby Jones is now firmly established as the long-suffering bursar of St Trinian’s, returning to the role for a second term of punishment at the hands of the young ladies in St Trinian’s 2: The Legend of Fritton’s Gold, now showing in cinemas.

But his connections with Abingdon School, where he was educated, run far deeper. And he was intrigued to hear from me that Felicity Lusk was to become the first female head in his old school’s 753-year history.

Ms Lusk, I explained, was moving in September to Abingdon from Oxford High School, the independent Oxford girls’ school where she has been headmistress for almost 14 years. “I did not know that,” the actor said, genuinely surprised.

The fact he had missed the news, splashed across a number of national newspapers as well as The Oxford Times, reflected just how busy Jones has been in recent weeks.

With the new St Trinian’s film, starring Colin Firth and David Tennant, complete, he is to appear with Julie Waters in Mo, a new television drama about Mo Mowlam, the former Northern Ireland Secretary.

He is also fresh from Sex & Drugs & Rock n Roll, the eagerly awaited film about one of his own heroes, the late rock star Ian Drury.

And then there is, of course, his commitments to another educational institution every bit as famous as St Trinian’s on the big screen, the Hogwarts School of Wizardary.

For Jones, 42, is the voice of Dobby, the mischievous house elf in the Harry Potter films.

Born in Oxford, Jones is the son of the larger-than-life character actor Freddie Jones, who has appeared in everything from The Avengers to Emmerdale.

He was brought up in Charlbury, where the family moved to from Kent more than 30 years ago, to renovate “an old doctor’s place”.

If his family background — his brothers Rupert and Casey also followed in the family business by becoming a television director and actor respectively — equipped him well for a career in acting, he says Abingdon School productions proved the most valuable training ground.

He certainly belonged to something of a ‘golden Abingdon generation’ as far as the arts were concerned, being there at the same time as members of the rock band Radiohead and the actor Tom Hollander, all of whom he well remembers.

His school background also came in handy when it came to the Harry Potter films, he tells me in all seriousness.

“I was able to draw on the experience of being a boarder at Abingdon. Schools can be a little bit like ships or villages. They are little microcosms, worlds within worlds, with their own rituals and their own rules. Abingdon, however, was never all that traditionalist. It always struck me as more of an ex-direct grant kind of school.”

But it was a school with a marked absence of girls. So, just how much more fun had it been, being on the set with Sarah and those glamorous gangsters in gymslips, rampaging across the Millennium Bridge, dangling from the Golden Hinde and rocking out in a mass dance routine in Liverpool Street Station?

“I know just where this is going,” he replied. “No, you are not going to get anything salacious out of me. I should warn you that my wife is a criminal barrister.

“But, yes, I did enjoy making it a great deal. I got to go flying around central London in a sidecar and to act at the Globe Theatre.” (The girls’ search for lost treasure ends up at the famous Shakespearian theatre, just in case you were wondering.) “The girls were all incredibly well behaved and supportive to each other. There was none of the bitchy and over-ambitious behaviour that you might have expected.”

The Girls Aloud singer, a young woman who certainly knows how to party in real life, it seems was pleasingly keen to learn more about the serious business of acting.

“She was great. There was all that stuff about her being a nightmare. But that was just not the case.

“My daughters (aged nine and seven) both loved the first film. So, that was another good reason to do it. I think girls just love what I call the ‘safe riskiness’ of St Trinian’s films.”

The fact that the first remake of the classic British comedy series grossed £12.5m at the UK box office alone, suggests he is right.

“As always when you remake a film, you worry about updating something that is so fondly remembered. But I think the writers did a good job.”

Jones speaks as a highly-rated writer himself, who has penned several impressive productions.

These include Missing Reel, a play famously based on his own personal experiences early in his acting career, when he landed a part in Notting Hill, the Richard Curtis comedy starring Hugh Grant and Julie Roberts. His cameo role as an over-eager fan of the Julia Roberts character appeared to suggest he had hit the big time.

But, shortly after filming, he received a crushing note from the producers regretting that his contribution had been cut from the final edit.

But instead of indulging in self pity, Jones resolved to immortalise the character the Notting Hill producers had seen fit to obliterate in his own anecdotal play about a small-part player’s attempts to mix it with the big boys. He obtained permission from Richard Curtis to show the suppressed material, while Hugh Grant appeared in the Radio 4 production.

His luck certainly changed when he landed a part in The Play What I Wrote, a celebration of the British double act Morecambe and Wise, written by Hamish McColl and Sean Foley.

The show’s key attraction was the appearance of special guest stars, such as Roger Moore, Ewan MacGregor and Harry Potter himself, Daniel Radcliffe. Jones received an Olivier Award in 2002 for his performance in the hit comedy.

In 2004, he performed opposite Helen Mirren in Elizabeth I, in the role of Robert Cecil, building on his fast-growing reputation as a chameleon-like performer with a knack for disappearing completely into his roles, with an uncanny ability to steal scenes even in small parts.

But the real step up came when he was offered the starring role in the Truman Capote biopic Infamous.

Mastering the voice of the tormented writer proved particulary difficult. “If a Brussels sprout could speak, that was how it would sound,” he told The Oxford Times. “A big part of the work was trying to befriend that voice in a way that I could use it so I could do it in different situations, not just when he was performing, but in more intimate scenes like in the prison with Daniel Craig.”

Some thought sheer bad luck intervened again to wreck another crucial opening in his career, as news emerged that a similar film about Capote was being made. If that were not bad enough, Philip Seymour Hoffman won best actor as ‘the rival Capote’.

For many critics, however, Jones’s performance, in which he looked like Capote’s twin, with a high-pitched voice and fey manner, was every bit as good as Hoffman’s.

“The director took a big chance, offering me the part. I never thought I would get to play a lead role in an American film. That film changed things for me. I have, in fact, been very lucky over the last five years. I’ve got to work with people whom I worshipped when I was younger.”

He has been directed by Kenneth Branagh (The Play What I Wrote); Oliver Stone (portraying Karl Rove, ‘Bush’s Brain’, in Stone’s George W Bush film W) and Steven Spielberg (the 3D adaptation of Tintin); while appearing with Judi Dench and Maggie Smith in the 2004 Oscar-nominated Finding Neverland.

But very early he came to the conclusion that the actor’s main concern should remain unchanged, whether you are in Elizabeth I or St Trinian’s 2. “The question stays the same. Your concern is finding the best way of showing the story. One of the comforting things for me is that films now seem to have a longer life because films get discovered on DVD or on television at different times. It means that they can get discovered years later.”

Given his reputation as a brilliant mimic, I wondered whether he would be playing the great Ian Drury in Sex & Drugs & Rock n Roll. In fact, he plays an evil character who traumatised the young Drury in a children’s home.

Millions more, however, like his own young daughters, will be eagerly awaiting his return as Dobby in the last Potter films.

After Abingdon and St Trinian’s, Hogwarts must have seemed the only place to go.