Piper has invested £8m in Be At One, valuing the business at close to £20m. The investment will aid an aggressive rollout of the brand towards an estate of around 30 sites.
It is thought that the main focus in the short-term will be the addition of further sites within London before the chain explores opportunities outside the capital.
Industry veteran Mark Derry, chief executive at Brasserie Blanc, will become chairman of Be At One.
Piper, which also backed the £9 million management buyin of the Tootsies chain in 1999, raised £107m through its fifth investment fund earlier this year.
Be At One was founded in 1998 by three former TGI Friday’s bar staff Steve Locke, Rhys Oldfield and Leigh Miller.
The trio's first site opened in Battersea.
Locke said: “We had an opportunity to work with a number of different investors but selected Piper on the basis of the team’s deep understanding of our brand and customers, their experience and reputation for success in the bar and restaurant space and for the value we believe they can add to our business during the lifetime of their investment.”
Piper partner Peter Kemp-Welch said: “We have an aggressive roll-out programme and believe the Be At One proposition has enormous potential.”
In May, the company appointed Zolfo Cooper to advise it on its investment options for future growth.
It opened its 12th site this week in Monument.
It hopes to open a further two sites in the capital before the end of next March.
Last November, the group reported like-for-like sales of £3.4m, up 8.4%, for the six months to 3rd October 2010, with overall sales up 25% on the previous year at £3.96m.
It is thought to turn over £10m a year.
The company has also been taking steps to strength its management team as it looks to gear up its expansion plans.
At the end of last year, it announced the appointment of Andrew Stones, formerly of Whitbread and JD Wetherspoon, as operations director.
It is also thought to be searching for a high-calibre financial director, after Zoe Tindall, formerly of YO!
Sushi, who was the group’s acting financial director, left to join Vietnamese-chain Pho.