The whims and prejudices of coaches and selectors kept Gregor Townsend on his toes during his playing days, but he clearly believes that any decent fly-half should be able to roll with the punches and deal with these little adversities.

Certainly, he is in no mood to allow any of his Glasgow Warriors playmakers to settle into the complacent belief that the No.10 jersey will ever be theirs by right.

So while most observers believed that Finn Russell had made an outstanding contribution to the Warriors' 27-9 RaboDirect PRO12 victory over Ulster at Scotstoun last weekend, Townsend has rewarded the 21-year-old's performance by moving him from 10 to inside-centre in the team to take on Edinburgh at the same ground tomorrow evening.

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Instead, the fly-half berth will be filled by Ruaridh Jackson, whose imminent move to Aviva Premiership side Wasps was confirmed only on Wednesday. With only three regular-season PRO12 games left, and with a home play-off now a tantalisingly close prospect, Townsend might have been expected to err on the side of continuity, but the choice of Jackson is a vote of confidence not just in the player's raw abilities, but also in his continued commitment to the club he has served for the past six seasons.

In fairness, Townsend has been consistently inconsistent in such matters. Over the past eight PRO12 matches, the coach has not once picked the same fly-half from one game to the next. In last season's chase for a play-off slot, he fielded Duncan Weir in the penultimate league outing and then trusted Jackson in the final match. And when the play-off took place, against Leinster in Dublin, he had Peter Horne in the pivotal role.

Jackson's style of play invited comparisons with Townsend when he made his senior breakthrough six years ago. Townsend also mentored him as he took his first, tentative steps in international rugby. The coach's admiration for the player is obvious, but it does beg the question of why on earth he should allow Jackson to slip away from the club.

"It was a difficult decision," acknowledged Townsend. "You believe in all the players you work with, especially the ones you have built up really good relationships with. I saw scenarios where both of them [Weir and Jackson] could still have been here next year, but these are the decisions you have to make. It is the reality of professional rugby.

"Next season will be a different scenario because Ruaridh won't be here. A lot of things go into these decisions. Budget is certainly one of them."

Stuart Hogg scored Glasgow's a pivotal try in their 26-20 win against Edinburgh at Murrayfield last December, but there is no place for him in tomorrow's matchday 23. Hogg has now served his time for the suspension he was given for being sent off for Scotland against Wales last month, but Townsend seems content with how his back-three have been performing, in defence as much as attack. Rumours continue to be heard about Hogg making a move to Ulster this summer, but reliable sources at both clubs have denied that the stories have any substance.

With all the other PRO12 teams taking the weekend off to give European rugby a clear run, a Glasgow win would propel Townsend's side into second spot in the table. Should they do so, they would oust Munster from a home semi-final position and Townsend has calculated that his side will retain that cherished berth if they can take two winning bonus points from their remaining three games.

"We are aware of that and there is nothing Munster can do to beat that," said the coach. "Munster have a couple of tricky games left, one of them being against Edinburgh away, and then Ulster at home. You never know what's going to happen in those games.

"But we also have a tough game here against our biggest rivals. We then have to go to Italy to play Treviso, who looked really good against Edinburgh a few weeks ago. After that we are against the ever-improving Zebre. First, though, winning against Edinburgh is the most important thing."

Whatever the permutations behind the scrum, there is a meaty and purposeful look to the pack ahead of tomorrow's game, with Al Kellock restored to the second row and Rob Harley coming back in on the blindside flank.

Kellock always seems to be at his stroppy best against Edinburgh and his absence - through injury - from the first leg of the 1872 Cup seemed significant as Glasgow struggled to impose themselves on their east coast rivals. Even Townsend suggested that his side was a little fortunate to win in that match.

"For the first 50 or 60 minutes they were the better team and we didn't play as well as we can," he said. "That was partly because Edinburgh played well, but we went away from the gameplan we wanted to play. But we kept playing for 80 minutes and took our opportunities."