The firm had offices in Norfolk and Suffolk and had been trading for 70 years building up to an annual turnover of £8m.
Directors told staff to down tools this week and current contracts will not be completed.
Chartered accountant Lovewell Blake has now been appointed liquidator.
The Knights Warner statement to the Eastern Daily Press said: “It was with much regret and sadness that the directors of Knights Warner Limited had to make the difficult decision that the company should cease trading on August 14, after almost 70 years of trading.
“The company is another victim of the effects of the economic downturn that has had a drastic effect on the construction industry.
“In order to remain competitive and win contracts, the company had to work to ever reducing margins and as a result of this and not being able to satisfactorily agree the final accounts on several large contracts, the continuation of the business was no longer viable.
“The company employed approximately 50 staff, working out of offices at Lowestoft and King’s Lynn, all of whom have been made redundant.
“Unfortunately, the immediate cessation of trading has meant that the company has been unable to complete work which was in progress on a number of sites across the region.”