Bankers have speculated that a sale could take place soon, given that 3i has been invested in Action since 2011 and said last year it had fielded multiple approaches from interested buyers for the jewel in its portfolio.

Action represents more than a third of 3i's private equity portfolio.

"There is no plan in the short term, in the next six to 12 months, to enter into a strategic review of the asset," Chief Executive Simon Borrows said on a call with reporters announcing the group's interim results.

3i, which is also invested in ferry operator Scandlines, said Action still has the opportunity for significant further growth as it rolls out a rapid store expansion programme targeting more than 2,700 stores and 10 billion euros (£8.9 billion) in annual turnover.

The firm increased its valuation of the Action stake, which analysts say is 44 percent, to more than 2 billion pounds, from 1.7 billion pounds as of March 31. It represents 35 percent of the value of 3i's private equity portfolio.

3i reported a rise in net asset value per share to 652 pence, from 604 pence as of March 31, 2017. Its share price was up 2.2 percent at 918.5 pence by 0935 GMT compared to a broadly flat FTSE 100 index <.FTSE>.

The group's total return - the change in the valuation of the portfolio, plus profits on disposals, plus any income from the portfolio and foreign exchange impact, minus the costs of the business - fell to 655 million pounds in the six months to Sept. 30, compared with 1 billion pounds in the same period of 2016.

The group attributed the decline to an exceptional previous period when the valuation of Action was bolstered by two approaches and foreign exchange gains from the fall of the pound.

3i, which was founded in 1945 in Britain, said its private equity portfolio's international investments, particularly in northern Europe and North America, now accounted for around 90 percent of the total by value.

(Reporting by Dasha Afanasieva, Editing by Lawrence White and Susan Fenton)