SNP Westminster leader Stephen Flynn is under investigation by parliamentary authorities for his use of stationery in a stunt attacking the Labour Party.

The party distributed mugs to journalists last month that mimicked Labour Party ads and said “control on family – what’s the point of Labour?”

The mugs were an attack on Labour leader Sir Keir Starmer’s refusal to commit to scrapping the two-child benefit cap if his party won the next election.

The attack was accompanied by a note on Mr Flynn’s own headed paper, which read: “The Labour Party has a new range of mugs in production.

“They’re made in China – just like Keir Starmer’s latest policy.”

The attack, the latest in a long line of SNP targeting of Labour as the party looks more likely to win the next general election, looks to compare the Labour stance on the two-child benefit cap to the one-child policy of the Chinese government, which ended in 2015.

As a result, Mr Flynn has caught the attention of the Parliamentary Commissioner for Standards.

According to the commissioner’s website, Mr Flynn is being investigated under paragraph eight of the House of Commons code of conduct.

The paragraph states: “Excepting modest and reasonable personal use, members must ensure that the use of facilities and services provided to them by Parliament, including an office, is in support of their parliamentary activities, and is in accordance with all relevant rules.”

An SNP source said: “This farce shows Westminster at its most absurd. The two-child cap has pushed 20,000 Scottish children into poverty but instead of worrying about the Tories and Labour Party both backing the policy, Westminster is attacking the SNP for daring to speak out.

“This shameful policy cost families in Scotland £95.7 million last year, with typical households losing £3,235 to £6,470 each, but instead of investigating the damage it has caused and Labour’s desire to back attacks on those in poverty, Westminster has launched an inquiry into the use of tiny handful of paper, with an approximate value of 2p.

“It tells you everything you need to know about Westminster’s skewed priorities.”