Police have been forced to intervene in Labour’s deselection row after two MPs had “sinister” cards delivered to their parliamentary offices wishing them “good luck with the new career”.

Officers from the Parliamentary liaison unit were last night probing how an unknown intruder was able to enter the office of one of the MPs and place the card, which contained details of an upcoming holiday to Cyprus, on their desk.

Both MPs were also sent a miniature toy replica of Thomas the Tank Engine, which left-wing supporters of Jeremy Corbyn have referred to as the “Deselection Express”.

The two Labour MPs affected, Joan Ryan and Gavin Shuker, have been outspoken critics of Mr Corbyn’s handling of the party’s anti-Semitism crisis, and were last week subjected to votes of no confidence by hard-Left members of their local constituency parties.

They are among a group of more than a dozen moderate MPs who fear that they could be deselected before the next election.

The Daily Telegraph understands that police officers investigating the incidents are working on the assumption that the culprits are Parliamentary passholders, and are now trawling through CCTV footage taken in nearby corridors.