On Tory MP John Bercow’s desk, angled so that only he can see it, is a framed photo of his pretty blonde wife Sally and son Oliver, 3.

Bercow, 44, was on holiday in the West Country with Sally, Oliver and the family’s newest arrival Freddie, when news broke of his controversial new role – working, er, for the government.

Some suggested that Bercow and fellow Tory MP Patrick Mercer were handing Labour a fabulous PR victory when both agreed to be government advisers earlier this month: Bercow as chairman of an inquiry into services for children with communication difficulties, Mercer as an adviser on security. “Grass-roots fury at Tory MPs lured by Brown”, screamed one headline.

But as Bercow eagerly leans forward to explain his decision to agree to the unusual request of the schools secretary, Ed Balls, it emerges that Oliver played a big part in his thinking, even as he emphasises that Sally, a Labour party member, did not.

“I don’t want to wave Oliver around like a teddy bear in all this,” says Bercow. Nonetheless, it was his son’s difficulties that sparked his zeal for the issue.

“A provisional diagnosis of our son suggested he had verbal dyspraxia. Since then we have discovered he is on the autistic spectrum . . . Sally and I were perfectly prepared to battle as hard as necessary to get him the help he needs but to date we haven’t had to: he is getting help [in a specialist language unit attached to his primary school] and making great progress.”

Since Oliver’s diagnosis 18 months ago, however, Bercow has discovered that many other parents have been nothing like as lucky in being able to nail down the intensive therapy needed to transform a child’s life. “I know of parents who have had to wage Kafkaesque battles to get help, some encounter obstacles at every turn, lots have a rough time.”

According to Bercow, around one in 10 primary school children is a sufferer from what is commonly known as SLI (speech and language impairment). Spotting the signs early is crucial: by the age of eight it may be too late. “If children get help early they can learn to communicate . . . If they do not, problems include emotional and psychological difficulties, lower education attainment, poorer job prospects and a possible descent into criminality,” he says bleakly.

He wants to make sure parents have a diagnostic “toolkit”: red flags to watch out for include children who are not at least babbling by the time they are two or find it hard to suck or blow.

Since Oliver’s problems came to light, Bercow – “I would not pretend for one moment that this was a special political interest of mine before then” – has been terrier-like in his attack on the gaping holes in Britain’s services: the closure of specialist centres by cash-strapped local councils and NHS trusts as well as the threat to language units such as the one Oliver attends. Parents face a postcode lottery in terms of services and there is a shortage of speech and language therapists nationwide.

Balls, who has a slight stammer himself, has responded to some of the demands Bercow has rained down on him in recent months, such as the request that every language unit in the country be centrally listed so that the information can be given out to parents. “If you don’t know what help is out there, how can you ask for it,” Bercow points out.

In fact it was Balls himself who approached Bercow, clearly taking a different line to Tony Blair, who once described the opposition MP as “nasty and ineffectual in equal quantity”.

“He said to me, ‘Look John, you have regularly taken up the issue of speech and language services in parliament over the last 18 months . . . Would you be interested in heading up a review of provision?’ ” “I said, ‘Ed, I would be interested but it is a relatively unusual thing to be asked to take up when you are in opposition. I must consult colleagues’.”

Bercow checked with both Patrick McLoughlin, the Tory chief whip, and the shadow schools secretary, Michael Gove. The pair agreed they would not stand in Bercow’s way although Gove wanted the announcement delayed a week – because of the febrile political atmosphere at the time, with Mercer also being wooed by Labour. Balls, who, says Bercow, is serious about tackling holes in SLI services, refused to change the timing.

Of course, Ivan, the eldest son of Bercow’s own leader, David Cameron, is severely disabled and Cameron has raised the question of adequate help himself. Isn’t the government’s handling of services for children with special educational needs an issue the Tories could have cashed in on? “I don’t think my taking this appointment has damaged my party,” he says firmly.

Yet there remains the question of how Bercow, who has moved massively to the political left since his youthful days as secretary of the immigration and repatriation section of the right-wing Monday club, will handle the inevitable grassroots backlash.

Two constituents have written disapproving of his move, he admits. He’s drafting a letter giving all of them details of the new job.

“I accept that if you shift your ground on issues it does fuel suspicion and anxiety,” he says. “But I am proud to be a Tory MP and want to remain one.”

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