Google’s rivals will have the chance to comment on concessions proposed by the US internet company to end an EU antitrust investigation, in a move that could force the company to improve its offer or even scupper a deal.

Complainants including Microsoft, online travel sites TripAdvisor and Expedia, newspaper publishers, mapping sites and price comparison sites, will have around a month to respond, the EU competition authority said today.

Several of them including lobby group ICOMP, which counts Microsoft and four other complainants among its members, said they were likely to press for more concessions.

Google, the world's most popular search engine, submitted its proposals earlier this month after the European Commission outlined four areas of concern about its business practices, saying these could restrict consumer choice and competition.

EU competition commissioner Joaquin Almunia said at the time he would try to reach a decision, including legally-binding commitments, based on Google’s proposals. But this could change, depending on the arguments made by Google’s rivals.

Without a deal, Google could face a hefty fine.

The EU competition authority said today that Google’s proposals included marking out its services from rival products in Internet search results and providing links to at least three competing search engines.

Specialised websites will be able to opt out from the use of all their content in Google’s own specialised search services and will also be able to mark out specific categories of information to prevent its use by Google.

Publishers will be allowed to control the display of their content in Google news and will no longer be obliged to use online search adverts exclusively from Google.

The search giant will also scrap restrictions preventing advertisers from transferring their search advertising campaigns to rival platforms.

If approved, Google's undertakings would be binding for five years in Europe and monitored by a trustee.