With a crunch European Cup clash at Wembley looming Saracens boss Mark McCall is highly concerned about the lacklustre form his side showed in their narrow victory over London Irish on Sunday.

McCall will hold an inquest this week into his team's below-par first half of the 15-11 win at Vicarage Road, and he made it clear that he expects an instant improvement when they host the Ospreys this weekend..

"We defended pretty well in parts, scrambled well in others when we fell off tackles." said McCall. "But it was a disappointing match, a scrappy match and we are disappointed with our first half performance. We were not up to our usual standards in certain areas and we'll definitely be looking at that during the week.

"Ospreys beat Munster on the weekend and will offer a big challenge. But we have played six games at Wembley and won five of them, our players really enjoy their outings there, as do our supporters," he said.

McCall paid tribute to London Irish who took the game to their hosts with ambition and some power.

"A lot of players put in a big shift for Irish out there and we had to defend well at times. But we have a number of guys in the walking wounded at the moment and hope to have Brad Barritt and Charlie Hodgson back for the weekend, while Schalk Brits will have served his suspension," he explained.

Irish head coach Toby Booth admitted his team came up short in terms of taking chances, but called for more unity between officials when it comes to scrummaging.

Time and again, the props in action questioned decisions on the grounds of consistency, and Booth believes it is wrong to leave referees to cope with so complicated an area alone.

"We need all three officials to work better as a team of three because a referee alone cannot have eyes everywhere." said Booth.

"Right now, it's a bit like those numbers that come out on balls late on a Saturday night. I believe there is a degree of 'guesstimation' when it comes to scrums and who is in the right and the wrong. Referees have a difficult job there and should be supported all the time by their assistant referees."

Booth made no excuses over the final result against Saracens.

He said: "They are the champions, well drilled and well coached. You must take points when you get as close to their line as we did on a number of occasions.

"The difference between the teams was taking chances. We left their 22 too often empty handed. Saracens kicked all of their goals and left us with only one point to show for our efforts.

Owen Farrell was the match-winner for Saracens, kicking all five penalties he was presented with by referee Andrew Small.

Homer and Dan Bowden kicked penalties for Irish who also scored the game's only try when David Paice was driven over by his pack four minutes from time.