Harlequins were so driven by the desire to reach the Heineken Cup semi-finals last April that they tried to cheat to get there. But having survived calls for their expulsion from this season's competition they rested their three England elite squad members for their first match – an eminently winnable one, against the Cardiff Blues – and left the Welsh capital without even a bonus point.

The next day, Sale arrived in Toulouse missing a number of senior players and found themselves 36–3 down within 50 minutes. On Saturday, London Irish will take on the Scarlets missing Paul Hodgson and Steffon Armitage. Why are clubs fielding weakened teams in Europe's premier club competition?

Under the new agreement between Twickenham and the Premiership clubs, which is worth £150,000 a year for every national squad member the teams provide, such players have to miss a match between the fourth and seventh weekends of a season. This coming weekend is the seventh.

When the Harlequins head coach, John Kingston, sat down last month to consider which match his England players – Ugo Monye, Nick Easter and Danny Care – would miss, he decided that three straight league defeats meant it would have to be in the Heineken Cup: the Blues away or Toulouse at home. Sale's director of rugby, Kingsley Jones, was in a similar position.

"Put yourself in my shoes," said Kingston. "We had only one point in the league and we were going to Newcastle. We had a crippling injury list and we had three fit players who were important to us." Monye scored the try at Kingston Park that ended Quins' losing streak and Easter got the winning try against Bath the next week.

"If the three had been available, they would have played against the Blues," said Kingston. "The agreement with England stipulates that we must rest players at any point during four matches and breaking it would lead to sanctions being imposed on us. It is the price you pay for having England internationals and the Premiership is as important to us as the Heineken Cup because it is how you qualify for Europe. It is different for sides in the Challenge Cup, because the opposition is not as strong."

Sale not only rested their three England squad players – Mathew Tait, Mark Cueto and Andrew Sheridan – for the trip to Toulouse, but other senior players too, including the club captain, Dean Schofield.

"The only way I will know if the selection was justified will be the result we get against the Blues," said Jones. "The game at this level is brutal: you cannot use the same squad on a Friday after you have played on a Sunday. We could have gone to Toulouse with the side that won in Clermont last year and still won nothing. It was a big test for our young players which they came through and we will have a fresh side for the Blues."

Sheridan had missed Sale's third game of the season; Care was absent from Quins' third. Only nine of the 32-strong England elite squad started the first three matches of the season and only two, Hodgson and Steffon Armitage, have started the first six, meaning they must rest this Saturday.

Mark McCafferty, the Premier Rugby chief executive, said talks between the clubs and England about the agreement were held this week. "What is important to remember is that there is flexibility. We are looking at the next group of fixtures which hold a rest weekend, between the end of the autumn internationals and the start of the Six Nations; we are widening the block to give directors of rugby more scope.

"We decided on a block, rather than a specified weekend, when drawing up the agreement for two reasons. First, it meant those clubs with a number of elite squad players did not have to rest them at the same time and, second, it allowed those sides who were in the Challenge Cup and had a relatively straightforward fixture a route outside the Premiership. "It was never our intention that the Heineken Cup would be affected and, while Harlequins and Sale made perfectly understandable calls last weekend, it is something that we need to look at. The whole point of the way the season is structured is that players go from Premiership to Heineken Cup to autumn internationals, stepping up in intensity each time. Martin Johnson [the England team manager] wants his players to be involved in the Heineken Cup for obvious reasons."

Clubs in England and France have a different mind set to sides from the Magners League. Their priority every season is making the Heineken Cup the following year: qualifying matters at least as much, if not more, than taking part, especially for sides, such as Quins, Sale, Bath and Gloucester, who make poor starts to the Premiership campaign: t. The league is certainly the priority in France. The Magners League, unlike the Premiership or the Top 14, is not haunted by the spectre of relegation and eight of the 10 sides qualify automatically for the Heineken Cup.

Well might the Munster outside-half, Ronan O'Gara, say last week that the focus for Irish internationals was Test rugby, the Heineken Cup and the Magners League, in that order. France have an advantage over England in that, with no salary cap, their clubs have deeper and stronger squads. Sale are not the only English side to have lost players of experience in the summer and to have replaced them largely with academy products. The cap means that the Premiership's top positions are never guaranteed. The current leaders, Saracens, are in the Challenge Cup. Four of the six sides in the bottom half of the table are in the Heineken Cup.

France's problem in Europe over the years has been the difference between the home and away form of their sides, as Perpignan, the national champions, showed last weekend when they lost away to the Italian champions, Treviso. Away victories are rare in the Top 14.

"The French tend not to prepare that well for away games," said the England and Brive fly-half, Andy Goode, whose side's defeat in Llanelli last weekend provided the Scarlets' second victory in 14 Heineken Cup matches. "We targeted winning our three group home games and picking up a victory away, which now means Northampton or Munster. I cannot understand the French sometimes."