UPDATE 1-UK's Sellafield plant detects elevated levels of radioactivity

LONDON, Jan 31 (Reuters) - British nuclear reprocessing plant Sellafield said it had detected raised levels of radioactivity at one of its on-site monitors and was operating at reduced staffing levels on Friday.

"As a result of a conservative and prudent decision, the Sellafield site is operating normally but with reduced manning levels today," it said in a statement.

It said only essential workers were being asked to report to work at the plant, which is on the coast of the Irish sea in northwest England. It said the levels of radioactivity detected were above naturally occurring radiation, but well below that which would call for any actions to be taken by the workforce on or off the site.

Sellafield only processes spent fuel and no longer produces power from nuclear. It is undergoing a decommissioning and dismantling programme, run by a consortium of British company Amec, French group Areva, and U.S. firm URS .

The UK energy ministry said it was in constant contact with the site and had no reason to believe the incident was more serious than Sellafield had indicated.