The Guinness Premiership provided all four semi-finalists last term, and bookmakers are predicting a repeat performance.

Tournament favourites Saracens launch their campaign on Sunday, while London Irish and Worcester - ranked second and third in the pecking order - face Italian opposition 24 hours earlier.

First into action will be fourth-favourites Northampton, who open against big-spending French outfit Toulon at the Stade Felix Mayol tonight.

And Saints should quietly fancy their chances, given Toulon’s run of four defeats in five games and the fact they are without major summer signings Sonny Bill Williams, Jerry Collins and Matt Henjak.

Northampton rugby director Jim Mallinder said: “The standard of our European pool is extremely high, right up there with the Heineken Cup.

“Toulon have a squad with plenty of international players and their coach, Tana Umaga, was one of the most respected All Blacks captains.

“Like ourselves, Toulon are a very ambitious club and the Challenge Cup is an important competition.

“It will be a massive occasion, so the challenge for us is to keep calm, stick to our game plan and put in plenty of hard work throughout the 80 minutes.”

Mallinder makes numerous changes from the side that beat EDF Energy Cup opponents Bristol 30-17 five days ago, with skipper Bruce Reihana, scrum-half Ben Foden, prop Tom Smith, hooker Dylan Hartley and number eight Roger Wilson among those who return.

There is no place though, for Carlos Spencer, with Stephen Mayler wearing Saints’ number 10 shirt and forging the half-back combination alongside Foden.

The second-tier European tournament continues with three games on Friday night, including Bristol’s trip to Montpellier and a testing opener for Connacht in Dax.

Each of the five pool winners will secure a quarter-final place, together with three best runners-up.