Two MPs say they are aware their local branches have been sent direct correspondence, with one to an address that was not in the public domain.
Momentum, set up after new Labour Party leader Mr Corbyn’s win, is considered a threat by some moderates who see it as a talking shop for planning the future deselection of MPs in favour more left-wing candidates.
One Yorkshire MP said both Momentum and CND must now be questioned on how they were able to contact a branch chair whose details were known only to a handful of local party members.
A spokesperson for Momentum said they obtained emails from ‘key contacts’ within constituencies, it was normal to attempt to contact branch chairs about campaign topics and that they do not consider it a data protection breach.
CND was contacted by The Yorkshire Post but did not provide a comment on how it had obtained email addresses.
The MP said: “The constituency Labour Party chair was contacted directly using contact details that were not in the public domain.
“Therefore there are legitimate concerns about how that information was accessed and how it was subsequently used.
“Given that this appears to have happened in many different areas, it is inevitable that a formal investigation will be requested to examine the circumstances of this serious data protection breach.
“The concern is that Momentum will be used as an organisation to undermine moderate MPs with a view to deselect and replace them with hard left Corbynites. Momentum is about developing that agenda and providing a forum for that debate.”
Momentum said its only correspondence to branch chairs had been to give information about their voter registration campaign.
The group was set up in October to continue the ‘energy and enthusiasm of Jeremy’s campaign’. A co-director is East Leeds MP Richard Burgon. However, it is not part of the Labour Party and they do not share mailing lists.
CND got in touch to offer the branch chair a speaker to talk to local members on “the issues around Trident and nuclear weapons”. Mr Corbyn is a vice-president of the organisation.
Another Yorkshire MP said: “I’m aware of the CND email and I think it’s a serious breach of the data protection rules.
“In regards to Momentum, the last thing the Labour Party needs is to go back to the bad old days of the 1980s with split and challenges to the integrity around MPs.”
It’s understood during the Labour leadership election campaign members emails were given to candidates. Campaign teams were then asked to delete this list, although Jeremy Corbyn naturally inherited the email database of Labour members after he won the election. However this particular branch secretary chair’s contact details were only known to a handful of local party members and they had never personally passed it on to CND.
The Momentum spokeseperson said: “Key contacts in constituencies and volunteers that we have all across the country have been able to gather contact details of key people within local parties so that we can co-ordinate our activities with them and offer support to them wherever possible.”