Britain’s youngest MP has used her first speech to Parliament to offer Labour some advice for choosing their next leader.

Mhairi Black, 20, said she came from a “traditional socialist family” but felt that Labour had rejected her and her beliefs.

“Like so many SNP members I come from a traditional socialist, Labour family. Like so many, I feel that it is the Labour party that left me, not the other way about,” she said.

“The SNP did not triumph on a wave of nationalism – it triumphed on a wave of hope – hope that we could have an alternative to the wave of Thatcherite neoliberal policies from this chamber, hope that representatives could genuinely give a voice to those that don’t have them. …

“I mention it in order to hold a mirror to the face of a party that seems to have forgotten the very people they’re supposed to represent – the very things they’re supposed to fight for.

“After hearing the Labour leader’s intentions to support the changes to tax credits that the Chancellor has put forward, I must make this plea through the words of one of your own, and of a personal hero of mine.

“Tony Benn once said that in politics there are weathercocks and signposts. Weathercocks will spin in whatever direction the wind of public opinion may blow them, no matter what principle they have to compromise.

“Then, there are signposts – signposts that stand true, and tall, and principles. They point in a direction and they say ‘this is the way to a better society and it is my job to convince you why’.

“Tony Benn was right when he said the only people worth remembering in politics are signposts.”

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Despite her criticism of Labour, Ms Black said the SNP was not the only opposition party and said she wanted to work with Labour to hold the Government to account.

The member for Paisley and Renfrewshire South said she had deliberately kept quiet and listened in the chamber in the months since the election.

She also joked that with her new access to expenses and the Chancellor’s cuts to housing benefit, she was “the only 20 year old in the whole UK that the Chancellor is prepared to help with housing”.

Some Labour MPs responded warmly to the wide-ranging speech, with MP for Hampstead and Kilburn Tulip Siddiq tweeting: "I may not agree with everything Mhairi Black said in her maiden speech but credit where it's due - it was well delivered, passionate & witty."