Heineken ambassador Will Greenwood takes a look at this weekend's Heineken Cup semi finals

The unpredictability of the Heineken Cup never ceases to amaze. Each and every year, this wondrous competition casts its magic spell over both players, supporters and even the most knowledgeable of pundits. As game after pulsating game, from grisly grey days of late October to the warm spring sunshine of a climatic final in May, unfolds, we are drawn in time and again by the possible permutations, nuances and every twist and turn. And at every stage, when you think you've settled on the group winners, or runner ups, or semi finalists, or even the final pairing that make that ultimate stage in May, you're so often left with the proverbial egg on the face, as time and again, shocks and surprises spring forth.

The beauty of rugby in general, but this competition in particular, is that so often results can go against the head and we were treated to what you'd have to class as two big shocks in the quarter finals. Both London clubs, Saracens and London Irish, overturned seemingly stronger opposition on the day and progressed to this weekend's semi finals, both team's first appearance at this stage.

So often rugby is a game where if you do your homework, get the basics right and execute well in key areas, you can overcome supposedly superior opposition, and you would have to say that both Brian Smith's Irish side, and Alan Gaffney's Saracens team did just that.

Unfancied as they were against the Perpignan powerhouse and the seemingly supercharged Ospreys, both teams refused to go quietly into the history of Heineken Cup 2007/8 and relished the challenge provided by their opposition. Make no mistake, it was a magnificent effort by both sides and it will require another Herculean effort again this weekend as they come up against the perennial achievers in this competition, Munster and Toulouse.