Robin Cook has indicated that he is ready to resign from the Rail Maritime and Transport Union in protest over an ultimatum to sign policy demands from the union's leadership.

Cook received £500 from the RMT last year towards Labour party expenses in his constituency.

Speaking in the Commons yesterday, Cook said he was "considering his position" and added that he expected his entry into the MPs register of interests - which lists the RMT donation - to be shorter next year.

Health secretary Alan Milburn said: "We can't and will not act as proxies for the trade union movement."