Sky News has learnt that Entain is working with advisers from Oakvale Capital on a prospective sale of the online poker business.

Industry sources who have been contacted about the sale said on Tuesday that they expected it to fetch around £150m.

Its valuation represents a huge cut on the £5bn that PartyGaming, PartyPoker's then parent, was worth on the day of its London flotation in 2005.

The business, which has seen a mass exodus of customers in recent years, is non-core to Entain's business.

As well as Ladbrokes, Entain owns Coral and a stake in BetMGM, a major US betting player.

Entain has endured a torrid period as activists have built an increasingly prominent position on its share register.

The company has seen its shares slump by more than 40% over the last year amid a deluge of regulatory problems.

It is currently being run by interim chief executive Stella David, having parted company with Jette Nygaard-Andersen late last year.

Shares in Entain were trading at around 739p on Tuesday morning, giving the company a market capitalisation of just over £4.5bn.

Entain and Oakvale both declined to comment.