The sector's biggest-ever deal comes as insurers struggle with rising claims and new challenges brought on by the COVID-19 pandemic and climate change. London-headquartered Aon, which clinched the deal a year ago to create the world's largest insurance broker ahead of Marsh & McLennan Companies Inc, offered concessions to the European Commission earlier this month. Following feedback from rivals and customers last week, the EU competition enforcer has asked for some tweaks but is unlikely to ask for more concessions, the people said. Aon could have faced a charge sheet called a statement of objections which sets out EU concerns if market feedback had been negative and if it had then refused to offer more concessions. This is not the case now, the people said.

Aon's shares reversed losses and gained as much as 1.2% after the Reuters story while Willis also trimmed losses and rose 2.9%. The concessions package includes selling a swathe of Willis assets, including its reinsurance arm and its German retirement benefits and consulting business, people with direct knowledge of the matter have told Reuters.

The concessions also include selling Willis' insurance broking activities in France, including French unit Gras Savoye, as well as in Germany, Spain and the Netherlands.

Willis' entire property and casualty business portfolio servicing large multinationals in those four countries and other European assets to service these clients, as well as its financial and professional lines, will also be sold.

The Commission, which is scheduled to decide on the deal by July 27, and Aon declined to comment.

(Reporting by Foo Yun Chee. Editing by Jane Merriman, Mark Potter and David Evans)

By Foo Yun Chee