Heineken Cup heads towards boiling point amidst the big freeze

Damned clever, the Heineken Cup. Europe's premier club tournament launches itself in mid-autumn with a fanfare of trumpets and an entire season's worth of razzamatazz, yet it keeps its true nature hidden until the dark days of winter, when the contenders play a series of back-to-back matches that invariably dictate the future course of the competition.

The central section of this season's pool stage begins tonight with Glasgow welcoming Toulouse, the champions, to the Arctic outpost of Firhill Stadium, but if the temperatures north of the border are at rock bottom, the mercury will rise very rapidly over the weekend when the leading clubs from four of the six pools meet in a series of highly significant contests.

Pool 1

Northampton have the best record of any side in Europe – one defeat in 13 matches spread across three competitions tells its own story – but Cardiff Blues, second in the table, will ask them some very difficult questions at Franklin's Gardens tomorrow evening, even though they have lost three top-drawer backs to injury. David Young, the head coach of the Welsh region, warmed things up a little in midweek by questioning the legality of the Midlanders' powerful scrummage, and while the Northampton hierarchy made a public show of laughing off the criticism, their private response was somewhat different.

Should the Blues win both matches, they will go into the last tranche of matches in January as hot favourites to win the pool and chase a home quarter-final. Northampton, on the other hand, could emerge with a clear advantage and still find themselves sorely tested by Castres, the dangerous outsiders from France who have not lost to anyone since their narrow defeat at Franklin's Gardens in the opening round.

Pool 2

Saracens considered themselves one of the tournament heavyweights back in October, since when they have managed only a single, miserable losing bonus point from two matches. They are still seething about their "home" defeat by Leinster at Wembley – a travesty of refereeing inconsistency, in their view – and are angrier still about copping a filthy great fine for broadcasting their frustration to the rugby world at large. But they are where they are (that is to say, bottom of the heap) and must beat the rather mysterious Parisians of Racing Metro tomorrow to stand an earthly of qualification.

The meeting between Clermont Auvergne and Leinster smack in the middle of France on Sunday should be a minor classic, and could be a major one if it revisits the heights of last season's quarter-final in Dublin. Clermont have a squad to die for and are unbeaten at home for more than a year, but the Irish province's stellar back division is something else again. Brian O'Driscoll and company have the class to make their hosts pay for slipping up in Paris in round two.

Pool 3

Four teams with grand ambitions, four teams with a 50 per cent record from the opening rounds. If this was predictable enough on the face of it – the pool looked tourniquet-tight from the moment it was drawn – both London Irish and Toulon have reasons to worry as they head into the December matches. The former have lost five games in succession, are positively sieve-like in their leaking of points and are in no obvious position to make a serious mark on this competition: quite a disappointment, given their excellent victory over the hard-bitten campaigners of Munster in the first match. The latter, meanwhile, should have lost to Ospreys first up and did lose in Limerick, by the small margin of 27 points, second time out.

It seems Munster and Ospreys have the winning of the pool between them, and they meet in Ireland on Sunday lunchtime before renewing hostilities in Swansea a week tomorrow. European rugby has been waiting for Ospreys to punch their weight almost as long as boxing has waited for Audley Harrison to punch something more solid than fresh air. The moment has surely arrived.

Pool 4

How Biarritz must fancy their chances of a seventh quarter-final in 10 years. Their victory at Bath on the opening weekend – a win gift-wrapped by their hosts and presented on bended knee – set them up nicely, and by claiming a bonus point in their follow-up victory over Ulster, they are in the best position of any side in the competition, especially as they have two matches against Aironi, the whipping boys from Italy, on their immediate agenda.

Bath are in a bad place, and must now travel to ... a bad place. Ravenhill is not the most sympathetic of venues for a travelling team struggling to work out where their next victory might come from, and if Ulster can beat the West Countrymen home and away, as they did last season, they could well make the knock-out stage as a pool runner-up.

Pool 5

Tigers in the bear pit? If it sounds gruesome, it is no less fascinating for that. Leicester know what it is to win in Perpignan – they managed it by a point at this precise stage of the 2001-02 tournament – but they have also found themselves on the wrong end of rugby Catalan-style and understand all too well how much it hurts. Victory at Stade Aimé Giral tomorrow afternoon would give the Midlanders a clear run into the last eight, even though Scarlets might conceivably spring a surprise in Llanelli next month. Defeat, on the other hand, will crank up the tension ahead of Perpignan's visit to Welford Road next week.

Pool 6

Toulouse will surely qualify one way or another, even though they are not in vintage nick at present. The question is this: can Wasps, lightweight up front but back in the winning habit none the less, take advantage of a soft draw by joining them in the last eight? The Londoners are no great shakes on the road and might have their share of awkward moments in Newport this weekend, but this is so obviously the weakest of the six groups, serious questions will be asked of them if they fail to qualify.