Franklin Mutual Advisers has written to Songbird to indicate it plans to accept any cash offer for its Canary Wharf Group shares, Qatar Investment Authority (QIA) and its bidding partner, U.S. investor Brookfield Property Partners, said in the document.

The bidders plan to retain key management in Canary Wharf Group if their 350-pence per share 2.6 billion pound ($4.04 billion) cash offer for Songbird is successful, they added.

Songbird owns 69 percent of Canary Wharf Group, established about 25 years ago on former docks as a new financial zone. It is also a part-owner of the "Walkie Talkie" skyscraper in the City, London's traditional business area.

It has previously rebuffed the bid, which followed an earlier 2.2 billion pound offer, saying it did not reflect the company's full value.

QIA already has a 29 percent stake in Songbird, while Brookfield has a 22 percent stake in Canary Wharf Group.

Franklin Mutual Advisers, meanwhile, owns approximately 7 percent of Canary Wharf Group, QIA and Brookfield said.

If their bid for Songbird is successful, they would make an offer for all Canary Wharf Group Shares not held by Songbird, they added.

The bidders said they had already had commitments to the Songbird deal from shareholders Third Avenue Management, Madison International and EMS Capital.

But any deal would have to gain the approval of Songbird's other major shareholders, including New York-based investor Simon Glick, who has almost 26 percent, and China's sovereign wealth fund, which owns 15.8 percent.

Shareholders have until Jan 29, 2015, to accept the offer, the document said.

(Editing by Simon Jessop, editing by Louise Heavens)

By Carolyn Cohn