The 25-year-old will make the move from the Sharks - with club having been keen on bolstering their second-row options following Smith's decision to join the New York Jets.

And Hargreaves, who has been capped four times but was overlooked for the World Cup, is relishing the chance to prove himself in the Premiership.

Hargreaves told the club's official site: "Everybody in South African rugby knows there is something special happening at Saracens, and I can't wait to get stuck in and make a contribution to the continuing development of the club.

"This is a fantastic opportunity for me at a crucial stage of my rugby career."

Saracens director of rugby Mark McCall is expecting big things from the powerhouse lock.

He added: "Alistair has a fantastic pedigree in SA rugby and we are confident he will flourish in our environment."