It started with a massage and developed into a highly sophisticated computerised scouting system which, if the claims are true, helped England win the rugby union World Cup, Northern Ireland defeat England's footballers, and cost at least one leading player his place in the team.

The product is ProZone and if you have not heard of it, you have not been reading match reports closely enough. From Sam Allardyce to Sir Clive Woodward, managers swear by it. It is not just the coaching fraternity either, Keith Hackett, the referees' chief, is another convert.

If Alex Ferguson wants to know how far Wayne Rooney runs, where to, and how quickly, he will reach for his ProZone data. So will Arsène Wenger if he wants to examine Cesc Fabregas's passing patterns. And when Blackburn travel to Stamford Bridge this weekend, Mark Hughes will call up Chelsea's set-plays and attacking movements, before plotting his game plan.

"I've always got my laptop in front of me and I can pull up any info," says Phil Brown, the Derby County manager. Brown, who became a believer while working alongside Allardyce at Bolton, goes on: "Here we go, Hull v Derby from Saturday. Inigo Idiakez, marvellous stats, same for Seth Johnson. If there's someone who's not so good, who's not playing in the right areas for example, I can call them into my office and show them 'this is what happened'. There's no hiding place. Someone might be great on the ball but with this I can check they are doing as well off it. You wouldn't pick a team on it but it can back up your gut instinct."

The same system showed Martin Jol that, contrary to his languid image, Michael Carrick was an influential breaker-up of opposition moves. It also, according to the rumour mill, led to one established international losing his place at another London club when his stats did not live up to his billing.

The genesis of ProZone came in the late 1990s at the Ramarena, Derby County's old training ground. Steve McClaren, then a young, innovative coach, installed a set of brown leather massage chairs on one of the Portakabins which dotted the site. Players sat in them before or after training and when they could not do the full work-out. As is the way with footballers, they passed the time bantering and reading the tabloids. McClaren thought the captive audience could spend this working time more usefully. He spoke to the chair suppliers and they looked into it.

From such an improbable beginning has football's Big Brother developed. The system uses a network of eight to 12 sensors around the stadium which plot players' movements every 10th of a second. This is backed up in the modest Leeds headquarters by a bank of staff, many of them sports science students, who note events such as set-plays and player runs, and check the computer identification.

Within 48 hours the DVD is sent to the clubs, who pay around £130,000 a year in subscription. For this they get fitness data and tactical information on everyone. Rooney's figures over several matches last season revealed, for example, that he runs 11.82km (7.35 miles) per match. Of that he spends four km walking, 4.8km jogging, 1.5km running, one km light sprinting and 500m sprinting. Ten per cent of his work is done in the defensive zone, a third in and around the opposition penalty box. He averages 105 touches in a match, 90 with his feet, 13 with his chest and only two with his head.

The referees suffer similar analysis. This followed a visit by Hackett to Sam Allardyce to discuss a controversial incident. Hackett went in armed with a video confident the official was right. Sam sat him down with ProZone and proved he was not. Hackett signed up.

Clubs increasingly use it to scout potential recruits, a facet which will grow as ProZone expands overseas. A consortium involving Ray Ranson, the former Manchester City and Newcastle United player, took over the company in 2004. It intends to expand into other sports and develop cheaper products for lower division teams - Scunthorpe's presence in the users' list is because they assist in training consultants who go on to work with Premiership clubs.

One incentive to be a subscriber is that the fitness data on your own team is confidential. The tactical information includes passing patterns, individual player movement, or, as in the case of the back four, collective movement. The match can be replayed, either on the manager's laptop or on a big screen, with the television footage and ProZone overview (which looks like Subbuteo from the air) running simultaneously.

Once managers, if they discussed a match over a meal, would shift the salt and pepper around. Sir Bobby Robson actually did this in front of me at PSV Eindhoven once. The game has moved on all right. Woodward recently invited Southampton's reserves (Harry Redknapp will not let him that near the first team) over for dinner at his flat. The entertainment? A ProZone re-run of their last match projected on to the dining room wall. A player's nightmare, and a coaching anorak's fantasy.

The stat pack

ProZone subscribers include:

FOOTBALL

Arsenal, Birmingham, Blackburn, Bolton, Charlton, Crystal Palace, Derby, Everton, Fulham, Ipswich, Manchester United, Middlesbrough, Scunthorpe, Southampton, West Ham, Wigan, Wolves.

Other clubs have it but have requested anonymity.

RUGBY UNION

England, South Africa, Northampton Saints