London Irish have been told they need to produce "the defensive performance of their lives" to have any hope of defeating three-times champions Toulouse in Saturday's Heineken Cup semi-final at Twickenham.

Alex King, who collected his second winners medal in the competition with London Wasps last year, is now part of the Clermont Auvergne squad that shocked French rugby last weekend by emerging 23-11 winners in Toulouse.

And now King has mapped out the successful Clermont game plan which could see the Irish produce an upset and reach their first Cup final.

King, who moved to Clermont last summer, said: "To beat Toulouse you need to have the defensive game of your lives because they have such impressive strike power and physicality. If you allow them to dictate play, then you are left chasing shadows.

"We set the tone for our victory from the first minute and anyone who watched that opening quarter will have been amazed at the ferocity of the battle for possession. We won every collision and dominated the contact area.

"The breakdown was just one of the key areas we pinpointed where we felt Toulouse could be vulnerable."

According to King, Clermont also picked out the Toulouse half-back pairing of Jean-Baptiste Elissalde and All Blacks scrum-half Byron Kelleher.

"Elissalde is an outstanding scrum-half but they are using him at No10 to accommodate Kelleher," he said. "When a player like Elissalde, no matter how talented, is operating out of position then he can be targeted.

"We put so much pressure on him that things behind the scrum started to unravel and he missed three drop goal attempts. He didn't get their back line going at all, which was a blessing given the massive pool of talent they possess." Clermont's success last weekend also involved matching Toulouse in the line-out, which was the trigger for so many of their attacks.

King added: "The Irish have two guys in Bob Casey and Nick Kennedy who could cause all kinds of problems on the opposition throw.

"We did the same and it was another major contributing factor to our win, along with a powerful scrummaging performance from our pack."

King's advice will be eagerly accepted by Irish, who are just as happy with the ball in hand, which makes the first of the Cup semi-finals - Saracens take on Munster at Coventry on Sunday - a potentially explosive affair.

Having only left English rugby last season, King is fully aware of the Irish strengths and weaknesses and sees the combination of England internationals Mike Catt and Shane Geraghty as one way the Exiles can exploit any hesitation in the Toulouse backs.

"With their belief in being able to score tries from anywhere on the pitch, Toulouse will always offer you chances," he said. "This commitment to attack can also be their downfall, although I maintain they are the best counter-attacking team in the world. With Irish determined to take the game to Toulouse, it has all the ingredients to be a cracking match."

King, who has been dogged by knee injuries in recent years, will quit rugby at the end of this season and hopes to go out with a French championship medal to add to the huge haul of trophies he collected with Wasps.

Many in France believe Clermont would have won the Heineken Cup if they had got through their pool, which also included Wasps and Munster.

"Having won the Cup twice I know what it takes to be the champions of Europe," he said." Here at Clermont, we didn't play well enough in the pool stages and this is a tournament that does not allow you to be off our game at any point."