Tournament organizers European Professional Club Rugby (EPCR) said that at the end of next season only the top seven clubs in the Celtic League will qualify for the 2018/19 Champions Cup, regardless of their country of origin.
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That replaces the current system, which insists that at least one club from each of Scotland, Ireland, Wales and Italy - the four nations that make up the Celtic League - is included in the seven qualifiers.
There have long been complaints that the presence of Italian sides gives clubs in the Champions Cup a chance to pile on the points and so makes it easier for them to qualify for the knockout stages than if they were in another pool.
Had the new system been in place this season, there would have been no Italian clubs in the 2017/18 Champions Cup given Zebre finished bottom of the Celtic League with just three wins from 22 matches, with domestic rivals Treviso tenth in the 12-team competition.
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Champions Cup qualification from the English Premiership and France's Top 14 remain unaltered, with the leading six clubs from both divisions entering European club rugby union's premier competition.
In a further change, the winners of the European Challenge Cup - the second-tier continental club tournament - will qualify automatically for the 2018/19 Champions Cup.
"These changes are designed to strengthen both the Champions Cup and the Challenge Cup," EPCR director general Vincent Gaillard said.
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