LONDON (REUTERS) - Britain's Boris Johnson said the Brexit withdrawal agreement with Brussels was "vassal state stuff" that would not protect Northern Ireland within the United Kingdom, and said he would vote against it when it comes before parliament.

Earlier on Tuesday, Prime Minister Theresa May's government said it had agreed a draft text of the Brexit withdrawal agreement with Brussels, which May will present to her senior ministers on Wednesday (Nov 14).

Johnson, who quit as foreign secretary over May's handling of Brexit, said he had not seen the full details but it had been widely trailed.

"It is vassal state stuff," he said.

"It is utterly unacceptable to anyone who believes in democracy.

"For the first time since partition Dublin under these proposals will have more say in some aspects of the government of Northern Ireland than London. I don't see how you can support it."