Jan 5 (Reuters) - U.S. refiner Phillips 66 said on Monday it had agreed to acquire the assets and infrastructure of Lindsey Oil Refinery in northern England following the site's liquidation, and will integrate the key facilities into its Humber Refinery.

The Lindsey refinery closed in July last year after previous owner Prax fell into insolvency, putting the 420 jobs at the site at risk.

Phillips 66, which did not disclose a deal value, said that after a detailed review during the bidding process, it had decided not to restart standalone operations at the refinery as the site is unviable in its current form.

Storage and infrastructure assets from Lindsey will be integrated into the Humber Refinery complex, which will improve supply flexibility and support traditional and renewable fuel production, Phillips 66 said.

"In the coming months, we will deepen our understanding of the new assets and develop strategic plans for their integration into the Phillips 66 Limited portfolio following completion of the transaction," a Phillips 66 spokesperson said.

The announcement follows a bidding process managed by FTI Consulting, which was appointed as special manager of the Lindsey oil refinery assets after the official receiver was named liquidator in June.

None of the bids that were credibly put forward had proposed a return to refining operations at Lindsey in the next few years, the official receiver said. 

The remaining 250 staff at the site are guaranteed employment until the end of March, the official receiver said in November, after redundancies began last September. 

"We are purchasing the assets of the Prax companies in liquidation and not the companies.  While we understand the impact on Prax employees, at this stage we cannot guarantee how many new roles will be created," the Phillips 66 spokesperson added.

UK Energy Minister Michael Shanks said in a statement: "This will expand the company's ability to supply fuel to UK customers, boosting domestic energy security and securing jobs – including hundreds of new construction jobs over the next five years."

The UK Department for Energy Security and Net Zero did not immediately respond to a request for follow-up comment on how the deal might impact UK fuel supply, and the status of the remaining jobs after March. 

"Lindsey oil refinery is a critical piece of UK energy infrastructure. Phillips 66 should not be allowed to just mothball the site and turn it into a glorified storage tank," said Unite union general secretary Sharon Graham. 

(Reporting by Pranav Mathur in Bengaluru, Robert Harvey, Shadia Nasralla; Editing by Shreya Biswas and Jan Harvey)