Jonathan Arkush, the president of the Board of Deputies, has expressed his “deep disappointment” at a tweet about the Balfour Declaration by an unnamed member of the UK’s mission to the United Nations.

The tweet, which tagged in Jonathan Allen, the UK’s deputy UN ambassador, read: “Let us remember, there are 2 halves of #Balfour, 2nd of which has not been fulfilled. There is unfinished business”.

The message was posted as finishing touches were being put to events to mark next month's centenary of the Declaration, which signalled Britain’s support for a Jewish homeland in the Middle East.

In an email to Matthew Rycroft, the UK’s UN ambassador, Mr Arkush described the tweet as “unworthy, hostile, unbalanced, negative and evidently intended as criticism of the State of Israel”.

He said he intended to lodge a formal complaint with Prime Minister Theresa May and Boris Johnson, the Foreign Secretary, and called for the message to be deleted and an explanation provided as to how it had come to be posted, and by whom.

The view expressed, Mr Arkush said, was “completely inconsistent with the United Kingdom’s declared policy to mark, commemorate and celebrate the Balfour Declaration (all terms used by the Prime Minister and other ministers in recent weeks)". 

The post would be greeted by the Jewish community with “strong dismay and virtually unanimous condemnation,” he added.