Anas Sarwar will take on Jeremy Corbyn over single market

Anas Sarwar has pledged to lobby Jeremy Corbyn to keep the UK in the European single market and customs union after Brexit if he is elected leader of Scottish Labour.

Ana Sarwar is the underdog in the Scottish Labour Party leadership contest. Photograph: John Devlin

Seeking to put pressure on leadership rival Richard Leonard over the UK’s withdrawal from the EU, Sarwar said it would be a “calamity” if the party loses membership of the single market and said voting to trigger Article 50 was a “mistake”.

He criticised his party colleagues, including leadership rival Richard Leonard – who defied the party whip and joined the Tories to back triggering Article 50 in a symbolic vote at Holyrood in February – saying: “We need a leader who fights a Tory hard Brexit, not one who backs them on hard Brexit.”

Sarwar’s single market stance puts him at odds with the UK leader, who has claimed that EU state aid rules could prevent Labour enacting its plans to nationalise public services if it gets into power. The Glasgow MSP is seen as the underdog in the race for the Scottish Labour leadership, with Leonard securing the support of the party’s biggest union backers, who have reportedly signed up thousands of their members to vote in the election. In a speech at The Lighthouse in Glasgow, Sarwar said he did not believe a hard Brexit was “inevitable”.

He said: “Let us not forget that Theresa May doesn’t have a majority. There are 13 Scottish Tory MPs in Westminster. They can help to stop a hard Brexit if they do the right thing by the people of Scotland they represent.

“We can vote down a bad Brexit deal in the UK Parliament.”

He added: “It was a mistake to trigger Article 50. It will be a disaster if we can’t secure transitional arrangements after 2019. It will be a calamity if we lose membership of the single market and the customs union.”

He added: “We will not just oppose a hard Brexit. Under my leadership, we will support remaining in the single market and the customs union.”

He added: “And let’s hear no more excuses about how a radical socialist plan will be held back if we remain in the single market. Tell that to the Dutch, the French and the Germans with their state-owned railways.”

He also warned politicians against exploiting fears over immigration, saying: “Our own party must never repeat the falsehood that it is immigrants who are responsible for downward pressure on wages.”

Sarwar acknowledged his plans could “put me at odds with some in the UK party”. Corbyn faced pressure at last month’s party conference to commit to remaining in the single market permanently, having called for continued membership during a post-Brexit transition phase.