London Wasps need to win their crucial Heineken Cup pool battle with Leinster at Twickenham tomorrow if they are to emerge from the shadow of arch-rivals Harlequins.

The Guinness Premiership champions are used to lording it over London's other rugby outfits but the dramatic improvement fashioned by Dean Richards at Quins means his side will qualify for the quarter-finals of Europe's top competition if they win in Ulster.

Even if they fail, Quins will guarantee a place in the last eight with a victory over the Scarlets a week later at The Stoop - a drop kick away from Twickenham Stadium, where they set a Premiership record by attracting 50,000 fans for last month's match with Leicester.

Wasps will have the backing of around 30,000 fans at HQ - they are charging full price rather than following Harlequins' discounted policy - and while that attendance is impressive, it still leaves their rivals with bragging rights over who are the biggest draw in London.

While Quins are odds-on to make the quarter-finals, Wasps have to win against Leinster and then possibly again at Castres a week later to keep alive their dream of winning a third European crown.

Having been hammered by Leinster in Dublin, Wasps face the prospect of seeing their great rivals Harlequins being London's only team in the knock-out stages.

The clash with Leinster has the look of a mini England v Ireland Test match, given the size of the international contingents in both squads.

However, neither side are firing on all cylinders, with the injured Tom Rees and Tom Palmer both missing for Wasps, who have only recently found form in the Premiership.

Leinster top Pool Two, thanks, in part, to their 41-11 hammering of Wasps in Dublin - a result which, three months on, still hurts the London side.

England flanker James Haskell said the players are determined not to be steam-rollered again.

Haskell added: "It did leave a bad taste in the mouth and the players were embarrassed to give away three tries due to charge downs and an interception. We need to create a bit of chaos because that's when we are at our most effective and we need to get back to that mentality. We are talking about sudden-death rugby and if we don't qualify for Europe next season, it will be a disaster."

Ian McGeechan has told his men they have to deliver on the Twickenham pitch which has provided the stage for their previous Heineken Cup and Premiership triumphs.

The director of rugby said: "We have to earn the right to be in the quarter-finals and we need to win tomorrow to keep the group alive. We are much happier with the way we are playing but now need to raise our performance level again otherwise we won't win."

Shaun Edwards, the Wasps head coach, has devised a new defensive strategy aimed at giving Danny Cipriani more protection as he kicks following a series of costly charge-downs this season.

Leinster will target the England fly-half but Edwards said: "It's not just about Danny. We have to deal with the kicks as a team and we have been working hard on a new strategy.

"Every time we have reached the quarter-finals of the Heineken Cup we have won the competition. At that stage of the Cup, it rivals football in terms of exposure and we want to be there."

Quins are facing a much-improved Ulster side and can dismiss their earlier 40-point success at Ravenhill against tomorrow's opponents.

A predicted wet-and-windy day will help Ulster's game plan of hoisting high kicks and attempting to cause mayhem backed by their vocal fans. Experienced men like England No8 Nick Easter will have to ensure the younger Quins players are not intimidated by the atmosphere which is going to be a world away from the pink explosion of fun and games they dealt with in Paris against Stade Francais.

A Quins victory will open the way for a vital home quarter-final tie in the knock-out stages.

Former Ulster and current Quins player Neil McMillan says his old club must not be underestimated.

The flanker said: "Their forwards are big, physical and very strong ball carriers, who are effective at the breakdown. Their backs contain a number of quick runners, such as wingers Andrew Trimble and Timoci Nagusa.

"Off the pitch, they have a very vocal and passionate crowd who make it very hard for any side to go and win there."