LONDON (Reuters) - Irish horse racing tycoons John Magnier and J.P. McManus raised their stake in Mitchells & Butlers (MAB.L: Quote, Profile, Research) to 5.12 percent on Friday, as a May 20 deadline on the pub and restaurant company's future draws closer.

The Irish pair's Elpida Group investment fund raised its holding from 4 percent.

Private equity firms, pub rivals and activist shareholders have been looking on with interest since M&B effectively put itself up for sale in January after losing 400 million pounds ($790 million) on a failed 4.5 billion pound property deal.

M&B said earlier this week it would announce the outcome of its strategic review on May 20.

Sources close to the deal told Reuters that private equity firms CVC and Blackstone have offered to take a 29.9 percent joint stake while buyout firm Permira and Bain Capital were also considering taking a stake in M&B.

(Reporting by Marc Jones; Editing by Rory Channing)