UPDATE 1-Old Mutual revamp could double share price-investor

* Top investor sees potential 5 bln stg gain in value

* Says sale of U.S. life unit alone would be disappointing

(Adds more quotes, further detail, background)

By Myles Neligan

LONDON, Feb 26 (Reuters) - One of the biggest investors in Old Mutual (OML.L) said the insurer could double its share price through a strategic shake-up due next month, piling pressure on the company as it prepares to announce its revamp on March 11.

Swedish activist fund Cevian Capital on Friday said the shake-up should focus on bridging the gap between Old Mutual's 113 pence share price and the combined standalone value of its businesses, which it estimates at more than 200 pence per share.

"I look at the share price today and I think the potential value of Old Mutual's different assets its probably north of 200 pence per share," said Martin Oliw, a partner at Cevian, which has a 5.8 percent stake and is Old Mutual's second-largest shareholder after AXA, which owns 6.1 percent.

"The potential is there, there is more than 5 billion pounds ($7.61 billion) in shareholder value to be unlocked."

Old Mutual declined to comment.

The company, a sprawling Anglo-South African conglomerate with insurance, banking and fund management operations spanning 35 countries, is under pressure to slim down and refocus as investors fret that its complexity is holding back its share price.

Oliw declined to comment on Cevian's preferred strategy for boosting Old Mutual's share price, but said the company must go further than the planned sale of its U.S. life business, reported earlier this week. [ID:nLDE61M21X]

"I wouldn't call that a real restructuring. If that's the only thing that comes out then I think it would be a disappointment," he said.

"At the very least we can expect the company to confirm the substantial upside potential in Old Mutual, and secondly to commit to closing this valuation gap in some way."

Cevian wants Old Mutual to conduct a root and branch review of its business, weighing up whether each of its units in turn should be retained or sold, Oliw added.

"Overall, we expect the company to go asset by asset, business by business, and look at all the structural options that are out there, versus the value of holding onto the business and improving it," he said.

Old Mutual's London-traded shares closed 3.75 pct higher at 113.6 pence on Friday. (Reporting by Myles Neligan; additional reporting by Clara Ferreira-Marques; Editing by Rupert Winchester)