SCOTLAND'S only Labour MP launched his deputy leadership campaign today, calling out the party's shadow chancellor as he did so.

Ian Murray, who was been a vocal critic of both John McDonnell and leader Jeremy Corbyn, took the opportunity to attack his colleague's decision to change Labour's "constitutional position on Scotland without telling anyone about it" last summer.

At an event with LBC's Iain Dale last August, McDonnell said Labour should not stand in the way of a second Scottish independence referendum taking place.

Murray said the shadow chancellor's move had been "disrespectful".

READ MORE: Ian Murray set to run for Labour deputy leadership position

He went on: "Let's never again have a senior member of the Labour Party coming to a fringe show at the Edinburgh Festival and changing our constitutional position on Scotland without telling anyone about it.

"That is not just disrespectful to the Labour Party, it is not just disrespectful to the Scottish Labour Party, its disrespectful to every single person who looks to the Labour Party for holding this UK together, and standing up for the key principle that independence for Scotland is bad for Scotland, and independence for Scotland is bad for the rest of the United Kingdom."

The Edinburgh South MP continued: "The Labour Party let down the voters of Britain last year. That can't happen again.

READ MORE: Labour MP Ian Murray likens indy debate to discussing English high street

"We must reach out and listen to every corner of this country and every type of person in our country.

"Our party can only win by winning support across the whole of Great Britain, and by becoming a broad church once again."

Following his speech, Murray told reporters: “I say this to all leadership and deputy leadership candidates: Please don’t come up to Scotland and talk about things that you’re not quite sure what you’re talking about.”

Murray is running against Rosena Allin-Khan, Richard Burgon, Dawn Butler and Angela Rayner for the deputy leadership position.

Both McDonnell and Corbyn will be resigning from their positions in the near future.