CELTIC: Despite reported interest from England, Gary Caldwell is urging Scott Brown to stay at Parkhead, hears Stewart Fisher

JOHN Collins and Paul McStay shared a midfield at Celtic but they had differing ideas of the meaning of that disputed term "ambition". Having won just a solitary Scottish Cup during his time at Parkhead, Collins opted to broaden his horizons and before long had a French title and Champions League semi-final appearance under his belt at Monaco. McStay, meanwhile, hung around the place for 14 years, his 678 appearances enough to earn him a place in the folklore of the club, even if the wider world would remain largely in the dark about his talents. But which of the pair had the more fruitful career? And, assuming he ever gets the choice, which route will Scott Brown choose to go down?

To borrow the parlance of American sport, the past six months have seen Scott Brown emerge as Celtic's most valuable player, with one newspaper reporting this week that Portsmouth were likely to test the Parkhead club's resolve with a £9m bid for the player. Gordon Strachan laughed off the matter, lurching into talk about martians and claiming this had as much reference in reality, but assuming the player's development continues at its current rate, interest from the Premier League will be real enough.

With three-and-a-half years remaining on his deal, Brown won't be going anywhere cheaply, but a watching brief on the saga should provide an interesting test case in the ever-changing dynamic between the Old Firm and the Premier League.

No footballer I have met has ever claimed not to be ambitious, but what exactly this means varies from player to player and is subject to historical variables over which the clubs themselves have little or no control. The Old Firm have always exploited their pre-eminent place in the soccer food chain to cherrypick the best talents from elsewhere in Scottish football, but 2009 sees them entering uncharted territory vis-a-vis their relationship with England's biggest clubs. The master-servant relationship is in danger of becoming the antithesis of those days when the likes of Terry Butcher, Trevor Steven, Chris Woods - or more recently Tore Andre Flo - could be lured north.

Fratton Park, Portsmouth, has a capacity of 20,328, almost a third of that Brown has grown accustomed to at Celtic Park, yet that is the select audience which could be viewing Brown's talents first hand if the transfer proceeds. With money likely to be freed up by the sale of Lassana Diarra to Real Madrid and likely departure of Jermaine Defoe, Brown could expect to more than double his reported £25,000-a-week contract and there is no doubt that Portsmouth could afford him. The question is whether Celtic can afford to let him go.

Gary Caldwell is an expert witness on the subject. Not only did he start off life in the academy at Premier League Newcastle United, he has now watched Brown develop in his spells first at Hibs, in the last six months at Celtic, and on the international stage with Scotland. His considered verdict on the matter is that not only will the club and chief executive Peter Lawwell do everything in their power to keep him and all the club's better players, but that Brown should be warned that life in England isn't everything it is cracked up to be in any case. Old Firm stars may soon have to weigh up the thrills of playing for one of the Glasgow giants against a significant shortfall in the wages that are available.

"The Premiership is great and there are obviously some big clubs, but I think overall people make it out to be this thing that maybe it isn't," Caldwell said. "There are some bad games and bad teams in the Premiership as well. The top four - or five if you count Aston Villa as well - are streets ahead and are very good teams, but overall it is maybe Sky TV and people like that bigging it up to something that it maybe isn't.

"If you look at it club by club then Celtic and Rangers are right up there with the top four or five in the league. So I think if players are linked with clubs they have to really consider that because it may well be a step down going from Rangers and Celtic to a lower Premiership club.

"I am sure the manager, the club and Peter will do everything they can to keep players," Caldwell added. "And if players are under contract, no-one can come in and just take them. I am sure our best players will remain at this club over the course of January. It is always a crazy month, everyone is always linked with everybody."

Six months ago, Brown was still dealing with the death of his sister from cancer, and couldn't be trusted to play from the start in his side's title run-in, but now it is impossible to imagine a Celtic team - or an SPL player of the season shortlist - without him. Those bursts from midfield are sighted less often, but so are the needless bookings, and rarely is he caught out of position. When that does happen, such as Aalborg's equaliser in Denmark, that must be the exception that proves the rule. At Ibrox last week, a few early misplaced passes gave way to a mature performance which helped turn the tide for his side.

"I think he has improved as a team player, as someone who fits into the team shape, system and how the team wants to play," Caldwell said. "At Hibs a lot of the time he was given free roles and just told to go out and play, but when you come to Celtic you have to win things, and to win things you have to be part of a team, and he has done that. He holds his position now when other times he might have charged forward and caused problems for the team."

Caldwell - whose own long-term future has yet to be resolved, with "the ball still in the club's court" regarding a contract extension beyond next summer - feels the crucible of pressure in which the Old Firm exist is part of the reason for his improvement. Compared to it, life in Portsmouth would be a picnic.

"I spoke to Kenny Miller when he went down to Derby and he missed that pressure," Caldwell said. "If you lose a game the whole world collapses around you. As a footballer it can be hard at times, but I think it also keeps you motivated. You would lose that as well by going to England."