Best known for its Regus brand, the London-listed company has received separate rival indicative bids from U.S. property investment firm Starwood Capital and British private equity fund TDR Capital, as well as an approach from American buyout house Lone Star.

IWG's shares were up more than 20 percent at 304 pence by mid-morning on Monday, having been as high as 311.9 pence.

The bid interest from three rival parties, disclosed following the close of trade on Friday evening, has raised the prospect of a "competitive auction" for IWG that could see the business bought for as much as 350 pence-a-share, or about 3.2 billion pounds ($4.4 billion), Peel Hunt analyst Andrew Shepherd-Barron said.

It comes after Canadian firms Onex and Brookfield Asset Management made a joint approach for IWG in December, only for takeover talks to fail at the start of February.

"This level of interest suggests much greater scope for competitive tension than the December 2017 proposal, and we now see IWG's going private as likely," Shepherd-Barron wrote in a note to clients. "We see 320 pence – 350 pence as achievable as a take-out price."

IWG's biggest shareholder is founder and chief executive Mark Dixon, who holds a 25.4 percent stake, according to Thomson Reuters data, meaning his stance will be key to a successful bid.

IWG has offices in about 3,125 locations, giving it a total of approximately 52 million square feet of workspace in more than 110 countries.

But it faces growing competition from rivals including WeWork, the co-working space startup backed by Japan's SoftBank Group Corp, and in October its shares plunged after it sounded a profit warning it blamed on a slowdown in London and the impact of natural disasters elsewhere in the world.

Annual pre-tax profits for 2017 fell 14 percent to 149.4 million pounds.

Under British rules, Starwood, TDR and Lone Star have until June 8 to make a firm offer or walk away from the company.

Bankers from JP Morgan and Investec are advising IWG.

(Reporting by Ben Martin; Editing by Keith Weir)

By Ben Martin