FILE PHOTO: Britain's Prime Minister Theresa May poses with European Council President Donald Tusk during a summit between Arab League and European Union member states, in the Red Sea resort of Sharm el-Sheikh, Egypt, February 24, 2019. Francisco Seco/Pool via REUTERS

LONDON (Reuters) - If Britain seeks an extension to the Article 50 Brexit negotiation period, Prime Minister Theresa May will write to the European Union’s Donald Tusk to set out why it wants the delay and for how long, the British government said on Thursday.

Britain’s parliament is due to vote later on Thursday on whether to seek a delay, after lawmakers rejected May’s Brexit deal for a second time earlier this week.

In a document setting out the parameters of any delay, the government said it would have to have a specific end date and Britain would remain a full EU member state during an extension.

“While Article 50 does not set out how either party should request an extension, the government believes it would be appropriate for the Prime Minister to write to the President of the European Council, setting out why the UK was requesting an extension and for how long,” the document said.