It is now confirmed by Google that it's to open its Shopping ads in Europe to Comparison Services businesses. Google will bid against these services companies ads.
The region includes EEA countries where Shopping ads are available: Austria, Belgium, Czech Republic, Denmark, France, Germany, Italy, Ireland, Netherlands, Norway, Poland, Portugal, Spain, Sweden, Switzerland , United Kingdom.

This comes hot on the heels of the suggestion it'll do this, and is probably aimed at appeasing the EU over antitrust.

It's far too early to know if this will actually work for the competitors, but it'll certainly be interesting to see.

Earlier Google May Open Up Ad Space to Competitors [webmasterworld.com]