LONDON - Billionaire currency trader Joe Lewis's Piedmont investment vehicle has upped its stake in pub and restaurant group Mitchells & Butlers , a former acquisition target, to over 25 percent.

Piedmont, which in October abandoned plans to make an offer for the group, is now M&B's largest shareholder with a 25.65 stake of the company from a previous level of 23.12 percent, regulatory announcements issued on Monday showed.

Crossing the 25 percent threshold gives a shareholder the ability to block special resolutions which require the approval of over three quarters of a company's share capital.

He's blocking off any moves organised by others, said an analyst who declined to be named.

It makes a situation impossible in which, for example, the institutions might have combined with the Irish investors to make decisions about the company which could have been made over Joe Lewis's head, he added.

Irish racehorse magnates John Magnier and JP McManus own a 24.23 percent stake in M&B.

Under takeover rules, Piedmont has to wait until mid-April to make any new approach for M&B, whose chains include Harvester and Toby Carvery.

Shares in the company, which has already rejected two bid approaches from Piedmont this year, traded up 0.5 percent to 230.6 pence at 1203 GMT, outperforming the FTSE 250 <.FTMC> which 0.2 percent higher.

(Reporting by Sarah Young; Editing by Lorraine Turner)