The future of scores of Tees Valley petrolium workers who survived a jobs cull of their colleagues less than three years ago was again plunged into doubt yesterday, with their parent company on the verge of collapse.

The Teesside operation of Europe's largest independent oil refiner Petroplus was placed into administration alongside other UK assets yesterday.

It came after the Swiss firm said talks with its lenders to extend deadlines for loan repayments had broken down and it would be filing for insolvency.

The latest blow comes almost exactly three years after Zurich based Petroplus put its North Tees refinery up for sale, later converting it to a terminal and storage facility and slashing around 75 jobs when a buyer could not be found.

Last night administrator PricewaterhouseCoopers (PwC) said no redundancies had been made at this stage, but the 60 workers who remain at the plant are now also facing an uncertain future.

In addition to the Teesside operation, which also oversees a research base in Swansea, Petroplus run Coryton oil refinery in Essex, where around 500 employees and 350 contractors are employed, was placed in administration yesterday.

Petroplus, which saw its credit rating downgraded by Standard & Poors earlier this month and suspended trading of its shares on Monday, had previously announced the temporary suspension of refining at Petit Couronne in France, Antwerp in Belgium and Cressier in Switzerland.

Despite the problems PwC said the UK business would continue to operate while a buyer is sought.

Administrator Steven Pearson of PwC said: "Our immediate priority is to continue to operate the Coryton refinery and the Teesside storage business, without disruption while the financial position is clarified and restructuring options are explored.

"Over coming days we intend to commence discussions with a number of parties including customers, employees, the creditors and the Government to secure the future of the Coryton and Teesside sites."

Linda McCulloch, national officer at the Unite union, said: ''One thousand jobs are at risk but we firmly believe that joint action by the owners and Government can help secure the business.

"We are in constant dialogue with Petroplus and their Swiss owners, and the UK Government about solutions to these developments."

Stockton North MP Alex Cunningham, in whose constituency the business is based, said: "It is a tremendous blow to a once thriving Teesside based business to find itself in administration and it is essential that everyone including the administrators PwC, the local authority and other organisations work together to find a buyer and secure the long term future of the business and its 60 employees."

Petroplus chief executive Jean-Paul Vettier said: ''We are fully aware of the impact that this will have on our workforce, their families and the communities where we have operated our businesses.''

The refining market has come under pressure in recent years as operating expenses and the cost of crude oil surge at a greater rate than the value of the products.

Petroplus reported a net loss of £265m in the first nine months of last year, while in December its banks withdrew a £675m portion of its £1.29bn credit facility.

The former BP-owned Coryton refinery, with a total capacity of 175,000 barrels of crude oil per day and which supplies 20per cent of fuel in London and the South East, has halted sales and told its staff it was unsure when supplies would start again.

Unite said that although crude oil was still being produced and the refinery operating lorries were not allowed to leave because of the insolvency arrangements.