Loch Fyne Restaurants, which operates 36 fish eateries south of the border, is selling itself for £68.1m cash to Belhaven-owner Greene King in a deal almost certain to trigger multi-million-pound gains for its most senior executives.

Suffolk-based Greene King was swift yesterday to highlight plans to double the size of the restaurant chain. This should be good news for the now separate and employee-owned Loch Fyne Oyster Company in Argyll, which still supplies the restaurant business that spun out of it in 1998 with fresh seafood.

The sale price is more than double the £33m paid less than two years ago by management and private equity firm Hutton Collins when they bought out the Loch Fyne Restaurants business, which has a big presence in south-east England.

The leap in value reflects the recent rapid and profitable growth of the chain, and the current demand for niche restaurant businesses with a nationwide brand. Such demand was also demonstrated recently by the bid battle for, and ultimate £104m sale of, tapas specialist La Tasca to a consortium led by property magnate Robert Tchenguiz.

A spokesman for Loch Fyne Restaurants declined to reveal how much the business's chief executive, Mark Derry, and fellow executives would make in the deal, but emphasised the management stake was spread among a "broad brush of people". Hutton Collins is believed to own about 55% of the business, with management therefore sharing a large but minority stake.

Derry and fellow director Ian Glyn, the main movers in the management team, are among those remaining with the business under Greene King.

Greene King, which bought Scottish brewer and pub chain Belhaven two years ago and said last month it was in talks with Loch Fyne Restaurants about a takeover, said it saw potential in the "medium term" to double the number of its latest acquisition's outlets.

It highlighted Loch Fyne Restaurants' current plans to increase its number of sites by around 20% within this financial year. These plans, which will be followed through by Greene King, include the opening of a new restaurant at Newhaven in Edinburgh later this month which will be its first in Scotland. Greene King added that the expansion of the chain would also involve the conversion of some of its pubs.

It noted some Loch Fyne Restaurants traded already in former pubs.

Greene King said Loch Fyne Restaurants "operates a proven food concept" which would help it to develop its own existing offer and would "deliver immediate entry into the premium-branded food segment".

It added that, in the 12 months to June 2008, Loch Fyne Restaurants' pre-overhead earnings before interest, tax, depreciation and amortisation were projected to be in excess of £10m. It projected post-overhead Ebitda of more than £8m in this period.

Greene King said the acquisition was expected to be earnings-enhancing in the first full year of ownership.

Rooney Anand, its chief executive, said: "Loch Fyne is a high-quality, well-respected British restaurant brand which gives us greater access to the premium end of the market and brings to our business further operational expertise. We have a strong track record of maximising the benefits from our acquisitions and this will be no exception."

Derry said: "The tie-up with Greene King is an excellent development for Loch Fyne. It gives us the opportunity to capitalise on our already strong reputation and to accelerate the expansion of our business.

"We're delighted to have found a buyer who recognises our strengths and whose style of management fits so well with our own."

Loch Fyne Oysters was founded near Cairndow in Argyll in the late-1970s by Johnny Noble, owner of Ardkinglas Estate, who died in 2002.

Two restaurants were opened in England in the early 1990s to introduce Loch Fyne products to a wider audience. The success of these openings led to an approach to Derry and Glyn to develop the restaurant business further.

Loch Fyne Restaurants was eventually spun out of Loch Fyne Oysters in 1998. In October 2005, management and Hutton Collins bought the business out of an Enterprise Investment Scheme.

The restaurant firm grew to 26 outlets by July 2006, and to 36 sites by last month. The restaurants serve more than one million customers each year.

Loch Fyne's menu is based largely on fresh seafood, with much of the produce still supplied by Loch Fyne Oysters.

Loch Fyne Oysters, which has seen its kippers sampled by Hollywood actor Clint Eastwood, was itself bought out by more than 100 employees in 2003 in a deal worth nearly £4m. The employee owners of this business inherited its lochside smokehouse, oyster fishery, shop and restaurant on the banks of Loch Fyne.