The dramatic collapse will send shock waves through construction that will hit many subcontractors.
Now more than 3,800 jobs are under threat at the self-styled “nation’s local builder”.
In a brief statement to the stock market, Rok, which was worth £450m in 2007, said it had asked the Financial Services Authority to suspend trading in its shares ahead of an administration.
Mike Jervis, joint administrator and partner at PricewaterhouseCoopers (PwC) said: “Our immediate priority is to urgently review the financial position of the company and seek a buyer of the businesses.
“Employees will naturally be concerned about their position, but they will continue to be paid if they attend work and perform their duties as normal.”
Rok’s problems started to emerge in August when it suspended its finance director after finding “serious failings” in the financial reporting of its plumbing business.
The contractor reported a £3.8m loss for the first half of the year.
The warning wiped out more than half the value of the building company.
Rok later lifted the suspension “immediately and without reservation” and exonerated the finance director for any blame for its problems.
It said a review of the business had concluded that problems in the division were “due to a scaling back of sub-contracting work from the private housing sector and a combination of weak operational, commercial and financial controls within that part of the business”.