Sept 25 (Reuters) - Ladbrokes owner Entain  (ENT.L) warned on its online net gaming revenues for the third quarter and the full-year on Monday, as the British gambling firm grapples with ongoing regulation in Britain, and slower growth in Australia and Italy.

Shares in the FTSE 100  (.FTSE)  firm fell as much as 8.2% to a 34 month-low of 969.2 pence by 0808 GMT.

The British government recently laid out long-awaited plans to crack down on problem gambling with proposals that would see new limits on online stakes, increased affordability checks on customers and a new statutory levy on betting firms to fund research, education and treatment for problem gamblers.

Regulatory headwinds were persisting longer than expected, Entain said on Monday, adding that adverse sporting results were also impacting its sports margins during September.

The owner of online brands bwin and partypoker said it expects third-quarter online net gaming revenue to be down by "high single digit percent" on a pro-forma basis.

It also expects group online gaming revenue for the full year to be down "low single digit percent" on a pro-forma basis. The company had earlier forecast annual growth in the low to mid-single digits.

Entain also said it would share details on the simplification of group structures and operations to improve its operational leverage and reduce costs, in its third-quarter trading update on November 2.

CEO Jette Nygaard-Andersen said the company was focused on capitalising on opportunities in the United States, where it jointly owns sports-betting service BetMGM along with MGM Resorts  (MGM.N).

The company  agreed to acquire U.S.-based Angstrom Sports for a potential consideration of up to 203 million pounds in July, as it looked to beef up BetMGM's offerings, particularly in the fast-growing markets of parlay and in-play wagering.

"Entain's revenue warning and restructuring announcement adds further uncertainty. A focus on optimised capital allocation may provide comfort around reduced M&A," Jefferies analysts said in a note.

($1 = 0.8170 pounds)