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* Activist Bramson's Sherborne vehicle owns 4.2 pct of 3i
* 3i says it has "wasted no time" to restructure
* 3i shares have risen 65 pct since mid-2012
LONDON, March 1 (Reuters) - Private equity group 3i defended its turnaround strategy on Friday after it emerged thatactivist investor Edward Bramson had increased his stake in thecompany.
Bramson, known for forcing through management shake-ups athis target companies, has bought 4.2 percent of 3i through hisinvestment vehicle Sherborne, at a cost of 105 million pounds($159 million), Sherborne said in a statement.
In January 3i revealed Sherborne and its broker Jefferieshad been buying shares, and in total owned a stake of around 1.6percent.
3i has been on a drive to boost its performance sinceappointing a new chief executive in May last year, cutting jobsand retrenching to its northern European roots in an effort towin over shareholders frustrated at poor share price performanceand weak results from its buyout business.
Shares in the group have gained almost 65 percent sincechief executive Simon Borrows launched his restructuring plan.
"We have wasted no time in implementing the significantorganisational and cultural changes that were needed," Borrowssaid in a statement.
"We are nine months into the first phase of restructuring at3i and our focus is now moving to the next phase...generatingvalue and sustainable performance for our key stakeholders."
A spokesman for Sherborne, which said in Friday's statementit may sell part or all of its positions in 3i, or add to it, declined to comment further.
Last year Sherborne raised 207 million pounds with the aimof investing in an unspecified listed company it consideredundervalued.
Sherborne said in a November statement its "investmentobjective is to realise capital growth from investment in atarget company", and that it would "only invest in one targetcompany at a time."
Media-shy Bramson has a history of taking on the managementsof companies he considers to be underperforming.
In 2011 he led a boardroom coup at British fund firm F&CAsset Management, ousting the chairman and pursuing aroot-and-branch shake-up of the 144-year old company after yearsof share price underperformance.
