BRUSSELS - "We don't have moods", the European Commission said on Monday in response to criticism from Britain's top EU adviser that the EU bore a grudge towards it for leaving the bloc.

David Frost wrote in British newspaper the Sunday Telegraph that the European Union should shake off its ill-will and build a good relationship with Britain as sovereign equals. 

However, the European Commission, the EU's executive body and which handles relations with Britain on behalf of the 27 EU nations, said it was an institution without swings of feelings.

"We never sulk, we don't have moods. We are an institution so we try to work on a day-to-day basis with a very, very even temper," the Commission's chief spokesman Eric Mamer told a news conference on Monday when asked about the comments.

Since Britain left the EU last year, relations between London and Brussels have soured, with both sides accusing the other of acting in bad faith in relation to part of their trade agreement that covers the movement of goods to Northern Ireland.

The Commission said last week it planned to take legal action over Britain's extension of a grace period for checks on goods coming into Northern Ireland from the British mainland. 

(Reporting by Philip Blenkinsop; Editing by Susan Fenton) ((philip.blenkinsop@thomsonreuters.com; +32 2 585 2869; Reuters Messaging: philip.blenkinsop.thomsonreuters.com@reuters.net))