JOANNA Cherry publicly backed Angus Robertson when he stood for SNP depute leader in 2016, it emerged today.

Robertson, the SNP's former Westminster leader, posted a photograph on Twitter this morning, taken outside the House of Commons, of Cherry alongside other SNP MPs holding up a sign “I'm nominating Angus Robertson MP. #Vote Angus".

Defending the right of MPs to show preferences in internal contests, Robertson wrote: "Endorsements are a key part of candidate selection process across the democratic world from the US Democrats to @theSNP. Here are some of the parliamentarians who nominated and endorsed me for the SNP depute leadership. #democracy."

His intervention followed leaked Whatsapp messages obtained by The National revealing Cherry told SNP MPs that they would be in breach of party rules if they endorsed a candidate in the Edinburgh Central selection contest.

Cherry, who is the SNP's justice and home affairs spokeswoman at Westminster, and Robertson have both entered the party's contest to be selected as the candidate to fight the seat of Edinburgh Central at next year's Holyrood election. Some 1200 members of the SNP branch will vote on who they want to be the party's candidate when the ballot opens in June.

Earlier today, The National revealed the dispute between Cherry and fellow MP Alison Thewliss, the party’s treasury spokeswoman at Westminster, over whether MPs could publicly support candidates.

READ MORE: Leaked messages reveal Joanna Cherry in SNP dispute over Holyrood race

Cherry, who represents Edinburgh South West, told MPs in a Whatsapp exchange last week that they would be in breach of party rules to do so. Thewliss, the MP for Glasgow Central, disagreed. The Edinburgh MP also argued that endorsements may not be in the interest of longer-term party unity.

Cherry's message was issued after Robertson's bid for the nomination was “liked” on Twitter by MPs Chris Law and John Nicolson and also backed by Westminster leader Ian Blackford's chief of staff Catriona Matheson.

The endorsements of parliamentary colleagues can work both for and against candidates in party contests.

Robertson won the 2016 SNP depute leadership contest after getting substantial backing from the party’s MPs and MSPs.

But Jeremy Corbyn's leadership bids did not get the backing of Labour MPs, though party members ignored the lack of support he had in the parliamentary party and voted overwhelming for him.

Last week Cherry sent copies of extracts of the selection rules to fellow MPs, suggesting they would be in breach of them if they made any endorsements.

Thewliss disputed Cherry's interpretation and said MPs could make endorsements though members of the party's ruling body the National Executive Committee (NEC) could not in their official capacity.

The National: Alison Thewliss clashed with Joanna Cherry over endorsements Alison Thewliss clashed with Joanna Cherry over endorsements

Cherry, the Edinburgh South West MP, posted: "Dear colleagues here are the Selection Rules – Scottish Parliament Elections 2021*. Para 11.3 is very important. Relevant parts of the Constitution: Members. 4 Membership. 4.1 The rights of membership include – ... (e) voting to select the Party's candidates at public elections ... Para 11.3 states that party officers and elected members ... must not seek to influence the votes of members by recommending a vote for a particular candidate or stating that their organisation is supporting a particular candidate.

"I will not be asking any of you to breach these rules in regards to Edinburgh Central and wd ask you not to do so re any other potential nominees."

Thewliss, the Glasgow Central MP, responded: "You've missed out 'acting in their official capacity' in that..."

Cherry replied: "Yes but if you tweet from your official MP account you are acting in an official capacity. Privately you are of course free to do as you please. There are good reasons for this rule. Whoever is selected the whole party needs to get behind. Hence the need to avoid obvious division. Which I am doing."

Thewliss then said: "My understanding of those rules is that it refers to elected members of the NEC, not MPs. It's in the section about organisational neutrality. I mention this because I highlighted this section at NEC."

Cherry responded: "Hhmmmm. Not my understanding but perhaps clarification can be sought."

READ MORE: Suspended SNP MP Neale Hanvey could be brought back in today

Asked for a comment by The National, Cherry said: "Selection is a matter for SNP members living in Edinburgh Central and them alone. I am standing on my record of hard work and action. I am very pleased to have the support of many of my MP colleagues but I would never seek to use them to influence the process. I hope my record of hard work speaks for itself."

Last week Marco Biagi, the former SNP MSP for Edinburgh Central, appealed for the contest to be conducted in a positive manner.

The seat is currently held by the former Scottish Tory leader Ruth Davidson who is stepping down before the election in May next year.

Both Robertson and Cherry are seen as potential successors to Nicola Sturgeon, and the selection contest has been described as a battle for the soul of the SNP.

Some see it as a contest over strategy on a second independence vote. Cherry wants MSPs to legislate for a consultative referendum without Westminster’s consent, to provoke a legal challenge by Boris Johnson, who has refused to give Holyrood the power to hold a second independence vote. Roberston favours Sturgeon's approach to exerting pressure on Johnson to grant a Section 30 order.

Nominations officially open in the Edinburgh Central and all other SNP internal selection contest for Holyrood candidates in April with the results expected in early July.

An SNP spokesperson said: "We’re still a month away from the start of the nomination process. Parliamentarians will be getting further guidance on when they can, and can’t, publicly express their support of an individual.”

Thewliss declined to comment.