Gordon Brown has insisted voting Boris Johnson out of Number 10 would be the first step in restoring “common decency”.
The former Prime Minister also said an increase in child poverty was a “moral stain” on Britain and should be a key election issue.
Brown addressed Labour supporters in Larkhall, part of the Lanark and Hamilton East constituency, where more than 4,400 children live in poverty.
Brown, who served as Prime Minister for three years and Chancellor for a decade, said: “In this election we must all speak up about the needs of the forgotten poor.
“Under the current Conservative government, child poverty is at record levels – worse than during the Margaret Thatcher years, worse than at any time in the past half century. It is why so many children’s lives and even entire communities are being destroyed.
“Child poverty is a moral stain on the fabric of Britain – and the tragedy of a generation of children going to school ill-clad and hungry shames our nation.”
He added: “A caring nation would increase child benefit substantially, raise the child credit, end the withdrawal of benefits from three and four-child families and guarantee that there is always enough housing benefit in place to pay rent.
“Boris Johnson’s departure from Downing Street on December 12 is the first step to moving our United Kingdom forward – united again in purpose, compassion and common decency.”
Lanark and Hamilton East is the closest three-way marginal seat in Britain, with just 360 votes separating the SNP, Conservatives and Labour at the last General Election.
The SNP ended a decade of Labour control in 2015 when Angela Crawley won with a majority of 10,100.
But in 2017, the Conservatives finished just 266 votes behind her and Labour’s Andrew Hilland 360 votes.
Mr Hilland, a lawyer and adviser to Gordon Brown during the Scottish independence referendum in 2014, said: “There’s a unifying theme of people saying it would be good if the politicians focused on the issues that matter to us.
“Those include investment in public services. There has been enormous cuts to public services in the last decade of the Tory government, with some of these cuts being passed on in the past two years by the SNP-led South Lanarkshire Council.”
Conservative candidate and Scottish Borders Council candidate Shona Haslam said indyref2 was the biggest issue on the doorstep.
She said: “People say they don’t want any more disruption. They want a period of stability and certainty. They have seen how difficult it is to extricate ourselves from a union of 40 years and how impossible it would be to extricate ourselves from a union of 300 years.”
The SNP’s Crawley said: “In 2014, we were promised in the Scottish independence referendum that a vote to remain in the UK would be the only way to stay in the EU.
“Lo and behold, two years later we were dragged out of the EU. Three years on, we find ourselves with no conclusion, no clarity, no confirmed deal.”