LONDON - A political declaration on Britain's future relationship with the European Union is still being negotiated, British Prime Minister Theresa May said on Wednesday.

May also said that if a full deal on Britain's future ties with the EU was not in place by the end of a planned transition period in 2020, there were three options to avoid a hard border in Northern Ireland: a so-called backstop, an extension of the transition or "alternative arrangements".

"We continue to negotiate on that future relationship to get the good deal that we believe is right for the United Kingdom," May told parliament.

(Reporting by Elizabeth Piper and Kylie MacLellan; editing by Stephen Addison) ((kylie.maclellan@thomsonreuters.com; +44 207 542 0401; Reuters Messaging: kylie.maclellan.thomsonreuters.com@reuters.net))