The Conservative party has started using the secure messaging service Signal for its internal communications with Tory MPs, following years of leaks from WhatsApp groups.

Signal, which is an alternative to Facebook-owned WhatsApp, prides itself on its ultra-secure privacy features and has an option to make messages automatically disappear after a set period of time, making it harder to retrospectively leak conversations.

The nonprofit open source service, which is endorsed by the likes of Edward Snowden, promises highly encrypted ad-free communications and pledges to ensure no one can read user messages or see their calls. Earlier this year the co-founder of WhatsApp gave $50m (£38m) to Signal to help improve the service.

Jim Killock of the Open Rights Group, which campaigns on internet freedoms, suggested the Tories’ switch to using Signal for party communications is ironic given the party’s longstanding campaign to introduce a backdoor on such messaging services for the benefit of the authorities.

Killock said: “It’s great to hear that Conservative MPs are learning about the virtues of Signal and secure private communications. Let’s hope they don’t also end up voting to make these private messaging tools wholly insecure with legally mandated backdoors that end up being used by police and criminals alike.

“I guess Priti Patel must be quite confused and alarmed as her party votes with its feet for secure messaging platforms, while she’s campaigning to stop them from protecting these very same users.”

In October the home secretary joined her Australian and US counterparts in writing to Facebook and demanding the introduction of a “backdoor” for the police and security services in WhatsApp, which she said would allow child abusers and terrorists using the service to be caught.

Facebook turned down the request on the basis that such a move would “be a gift to criminals, hackers and repressive regimes, creating a way for them to enter our systems and leaving every person on our platforms more vulnerable to real-life harm”.

A Conservative spokesperson said the real justification for their MPs to use Signal was operational, rather than for security reasons. With so many Tory MPs elected at the last election, it had become impossible to fit them all in a single WhatsApp group, because they are currently capped at 256 members.

While this worked until the last election, with only a few MPs missing out, the party’s electoral success means it now has 365 MPs to coordinate – a number that Signal allows to be put in a single group.

In common with much of society, the WhatsApp group has become a staple of organisation and plotting in Westminster in recent years, with screengrabs of communication regularly leaked to journalists. Some MPs have reached the point where they actively post messages in a popular WhatsApp group in the expectation that they will swiftly be passed to reporters – effectively turning them into press releases.