The men exiting Summer Row

They are the bosses of two £1billion property and construction empires based in and around Belfast, which is also home to Summer Row's main developer, Multi.

The Express & Star told how the future of the showpiece 85-store complex to be anchored by Marks & Spencer and Debenhams was in doubt, after a crucial finance deal with Irish backers collapsed.

Now we can reveal details of the NI Investors consortium which pulled out of a deal to pump £150 million into the city development after a year of negotiations, leaving council chiefs devastated.

The consortium comprises two major backers, Lagan Group and MAR Properties, along with a housebuilding firm called Windsor.

Lagan is owned by brothers Michael and Kevin Lagan, who feature in the Sunday Times Rich List thanks to their £928million construction fortune.

MAR, which also wants to build a multi-million pound aviation park at the Wolverhampton Airport site in Halfpenny Green, is headed by chief executive Robin Horner along with directors Noel Murphy and William Rush.

The two businesses have worked together previously on several projects, forming a joint venture called Lagmar.

Their decision not to invest in Summer Row threatens the future of the centre, which cannot be built unless developer Multi can secure match-funding.

Multi Development believe the deal to sell 49 per cent of the project to the NI Investors consortium had "fallen away" after a year of negotiations.

Paul Sargent, Multi's managing director, blamed the credit crunch for the failure to seal the finance deal which means construction cannot get under way by March next year as planned.

Currently the Irish businessmen are all lying low, unwilling to talk about their decision to abandon the Wolverhampton scheme.

No-one was available to comment from Lagan Group's Clarendon Dock headquarters in Belfast.

Similarly no-one was available to speak at the offices of MAR in Bangor, County Down, just outside of Belfast.

But a company spokesman said: "Under a confidentiality agreement MAR Properties have signed with Multi Development, they are not free to make any comment on the project."

The Lagan Group has developed from the company formed by the Lagan family more than 40 years ago.

It remains in private hands, controlled by brothers Kevin, aged 58, and Michael, 52. The most recent Sunday Times Rich List estimated the brothers were worth £928million.

Lagan is now a diverse group of around 29 businesses involved in the manufacture and supply of construction materials, civil engineering, surfacing, house building and property development.

Last year it made a profit of around £57million after boosting its turnover by £78million to £478million. The business employs a total of around 1,300 people.

MAR also bought the Wolverhampton Airport site at Halfpenny Green from previous owners City Hopper in 2006.

Chief executive Robin Horner, a qualified solicitor and chartered accountant, was recruited to head the business from investment bank IBI Corporate Finance in Belfast two years ago.

He sits on the board alongside founder directors Noel Murphy and William Rush, who set up the company in 1997.

MAR also owns Blackpool Airport and has an extensive interest in shopping centres across the UK. In one six-month period it made around £15million profit, from the sale of shopping centres in Norwich and Glasgow.

It started out as a site developer and housebuilder in the North Down area of Northern Ireland, but now controls an investment portfolio across the UK and North America valued at around £1 billion.