Isis Equity Partners, the private equity group, is in talks to acquire a stake in Pho, the highly-thought of Vietnamese fast-casual concept led by Stephen and Juliette Wall.

It is understood that Isis, which has previously invested in the clothes retailers Bonmarche and Fat Face, is in advanced stages of talks with the six-strong restaurant group, with plans to invest up to £8m in the chain.

If successful it would mark the first move into the casual dining market for Isis, which was previously linked with the Loch Fyne restaurant business over six years ago.

Last August, Pho appointed Zolfo Cooper to advise on its investment options for future growth, as it looks to grow its estate to up to 25 sites over the next four years.

It is understood that the group, which includes Ed and Tom Martin, of ETM Group, the food-led London pub operator, as investors, has already received a number of approaches from private equity groups over the last 12 months

The business, which is thought to be close to signing on a further site in the capital, was founded in 2005.

Pho, which is based on the Vietnamese national dish of noodle soup (pronounced “fuh’), has five locations in London, plus one in Brighton, its biggest with 130 covers.