LONDON, Feb 3 (Reuters) - Britain should tighten rules on admitting highly skilled economic migrants from outside the European Union so they do not take jobs that could go instead to British graduates, immigration minister Phil Woolas said.

Woolas's proposal comes as the use of European workers at a British refinery has prompted strikes at energy plants across the country by Britons fearing job losses. Trade unions asked the government on Tuesday to tighten the law on the use of foreign workers.

In an interview in Wednesday's Independent newspaper, Woolas said the government should toughen Britain's points-based system, which allows scientists, lawyers and others from outside the EU to enter to the country to search for work.

"The points-based system that has been introduced allows us to toughen the criteria, and clearly in the economic situation that is something it is beholden on us to do," the paper quoted Woolas as saying. "We want to maintain the highest possible levels of British graduate employment."

The paper said the proposal had been under consideration for some weeks and ministers insisted it was not a reaction to the refinery row. The daily said the plan would be discussed by cabinet ministers as they draw up a package of immigration measures over the next few weeks.