In the end, the mathematicians were not required. Wasps had to win in south-west France in order to enter the equation for a quarter-final place as one of the Heineken Cup's two best pool runners-up, and it proved too tough a task. The Premiership champions were ­seething afterwards, feeling they had let Castres off the hook with their poor finishing. They did indeed spill two clear-cut chances in the second half, the second of which could have put them eight points clear, but Castres were well worth their win. The French club, who had no chance of progressing, missed a few chances of their own and were twice held up over the line by a ­desperate Wasps defence.

And so another prospect of silverware has been closed off to England's champions. Their only hope now is to make the Premiership play-offs and win the title from there, a concept they know more about than any. But they wave ­goodbye to 15 players, who are off on various assignments with England's elite squad, the Saxons and Ireland. There will be an empty feeling in the camp this week in more ways than one.

Here they were killed off by a try with barely five minutes to go. They had just taken the lead for the first time, when Dominic Waldouck showed commendable skills to finish off a quickly-tapped penalty. Shortly after that Dave Walder, on for Danny Cipriani, broke clear, but his pass was spilled by Mark van ­Gisbergen with the tryline laughing at him.

It felt as if they had blown it. Paul Sackey had been implicated in Wasps' other great miss earlier, when Rob ­Webber fumbled his unforgiving inside pass with the line at his mercy, and now Sackey was down injured as play continued. Thomas Bouquie was able to hare towards the line, through a hole that might have been filled by the stricken winger. Bouquie went clean through Van Gisbergen's weak attempt at a tackle and round for a try between the posts. Now the game really seemed over.

Shaun Edwards, Wasps' coach, was furious at the way Bouquie was left to run free. He mused afterwards that a player should never stay down while he is in defence, unless he has "a very, very ­serious injury". Sackey said afterwards that he was fine, it was just a numb buttock. That was news that may not have pleased his coach as much as it should.

Wasps mounted one last tilt, but ­Castres absorbed their efforts with a bit to spare. Quite how they find ­themselves struggling only one place and two points above the relegation zone in the French championship is hard to fathom on days like this, or the one before Christmas when they beat Leinster, the eventual pool winners.

Two first-half tries formed the bedrock of their efforts and saw them through until the 66th minute, when Wasps took that hopeful lead. Both scores came in an opening half-hour that Castres ­dominated. The game may have been dead for them, but they fielded more or less their strongest side, a blend of strapping locals and ­strapping natives of the south seas.

Bouquie, one of the former, galloped over from full-back for the first of his two tries after quarter of an hour, after another local, Lionel Mazars, had been put through by the Australian centre Steve Kefu. ­Cipriani replied with a ­penalty shortly afterwards, but it was a brief ebb of the tide. Chris Masoe, an All Black flanker, no less, and superb throughout, was next over, the path cleared for him by the Samoan Joe Tekori bursting off the back of a scrum.

That made for a 14–3 scoreline, before ­Cipriani scorched home for a fine individual try just after the half-hour. For those who like Cipriani-watching, that was as good as it got. He again did away with his headguard, a trend that should please his fans, but otherwise he was inconspicuous. As was the No8 James Haskell, another of Wasps' great young talents whose future is as yet unknown.

How Wasps will balance their books and manage to satisfy the wage requirements of those two while saying goodbye to yet another shot at silverware remains to be seen. There may yet be work for those mathematicians after all.

Castres Bouquie; Bonnefond, Kefu, Mazars (Sanchou, 61), Cabello; Teulet (Lagardere, 80), Tillous-Borde (Senio, ht); Hoeft (Terrain, 61), Giorgadze, Ducalcon (Staibano, 55), Nallet (capt; Michaud, ht), Kulemin, Malonga (Faure, 53), Masoe, Tekori.

Tries Bouquie 2, Masoe. Cons Teulet. Pens Teulet 3.

London Wasps Van Gisbergen; Sackey, Waldouck (Voyce, 67), Flutey, Lewsey; Cipriani (Walder, 68), Reddan (Simpson, 77); Payne (Leo, 63), Webber (Ward, 59), Vickery (capt), Shaw (Skivington, 55), Birkett, Worsley, Betsen, Haskell.

Tries Cipriani, Waldouck. Con Cipriani Pen Cipriani.

Referee A Lewis (Ireland). Attendance 7,223.