Downing Street's health policy adviser is a man of mystery and intrigue.

He is shrouded in mystique, viewed as a 'natural twin for Blair' and is rated by some as more powerful than ministers.

How much can HSJ find out about the highly secretive Downing Street policy adviser on health, Robert Hill?

Officially, the answer is nothing - despite the fact that he is seen as the key player behind some of the most radical changes in the way healthcare is delivered.

Many describe him as the architect of the primary care reforms and walk-in centres. Some suggest he has recently been pushing public-private partnerships for pathology services.

But Mr Hill is not a civil servant, and the only person he has to account to is his boss: the prime minister. HSJ's request to interview him was declined.

His background includes spells as a union official with NUPE and Unison, a management job at the Audit Commission and a period at Labour's Millbank headquarters, when he was despatched to deal with councillors seen as too left-wing and troublesome.

It is precisely that lack of a long history in health practice or policy that means he is 'free from baggage and can see things through the consumer's eyes', according to Ray Rowden, Labour Party member and honorary visiting professor of nursing at York University.

He names the special adviser as the 'driving force' behind walk-in centres for primary care. If it 'doesn't get passed' by him it doesn't happen.Make no mistake, this man has the ear of the prime minister.

Professor Rowden reckons the civil servants forced to work around Mr Hill 'hate' his influence. So why does the private sector like him so much? 'He's not an ideologist and they find it easy to deal with him.'

He sees Mr Hill's role as 'working on the different models' for providing healthcare. These will 'He is one of the most powerful behindthe-scenes players in British healthcare' be implemented if in three or four years' time nothing much has changed for the better, despite the new money. 'That is where Hill comes in.'

One private sector source describes Mr Hill as a 'very able man, a technocrat and committed Christian'.

Indeed, the policy advisor worships at the same church as that other mover and shaker, private health sector businessman Dr Chai Patel.

'He understands the Blair revolution and is one of the most powerful behind-the-scenes players in British healthcare, ' the private sector source says.

The Guardian's 'Power 90' survey named Mr Hill the most influential individual in health apart from ministers.

The private sector insider says that Mr Hill is 'methodical, has an eye for detail' and sees the NHS as a funding mechanism which has to 'chime with the principles of equity'. But he also sees it as 'a brand'.

When it comes to personality, 'he's personable but reserved and a lot of people think he's so quiet that he appears to be distant and aloof '. He's a 'natural twin for Blair and That is why he has so much power'.

What is his Achilles' heel? 'He looks so much at the detail. Even with the best will in the world There is a question about his ability to keep ahead of events.'

Health secretary Alan Milburn has mixed views on him, according to our rather well-connected private finance source: 'He sees Robert as a good friend, and so long as Robert likes him he will be someone who helps his career. But It is a relationship of respect, not sycophancy.'

Unison's head of health Bob Abberley thinks the 'accessible' Hill has 'made a valuable contribution'. If there is a criticism, 'I think he's too influenced by what he has learnt in the US'.

'I think he fundamentally believes in healthcare free at the point of use and funded by taxation. But I think he very much feels he wants to test basic principles to see if they stand up.'

But a second union source somewhat muddies the picture of Mr Hill as a bright spark. 'He started life as a union official with NUPE and then moved to Millbank, where he got a hard-nut reputation for sorting out left wing local authorities and then ended up where he is now.

'But his background does not equip him for what he's doing.He's out of his depth and at some point he'll go off to the private sector.He was a very ordinary union official rather than a rocket scientist. I've met him on a number of occasions and he's not impressed me. He's now a powerful gofer.'

But the same source sees Mr Hill as the 'driving force on plans to privatise large chunks of pathology services' and closely involved in 'the whole publicprivate partnership thing and the relationship with the drugs companies'.

What is known is that he also wants to open up the British Medical Association and other professional groups to supplyside reforms.A senior doctor, who confirms that Mr Hill 'invented NHS Direct and the walk-in centres', says 'nothing happens in the Department of Health without his say-so'.

A man of 'very small humour', he encourages people to 'show leadership, which in practice means agreeing with the government'.

'He actually does keep some quite good tabs on things, but unfortunately I am quite convinced that what he does in that line is not necessarily very systematic in terms of the way he gets evidence.He's told things because he wants to hear them.'

Ministers at the DoH have 'a lot of scrutiny going on', he concludes.

'Ministers are not at liberty to run their business as they see fit.

They have two overseers - Robert Hill and the Treasury.'Add to that a prime minister with his radar screen set firmly on health.