Rebecca Long-Bailey's Labour leadership credentials took a blow on Sunday (13 March) following her appearance on BBC One's Andrew Marr Show. The shadow business secretary failed to explain how her party would fund £63bn worth of spending pledges, including scrapping university tuition fees in England and Wales.

"The cost is all based on either red book numbers, official numbers, or Labour's own costing and it come to something like £60bn of extra spending," Marr said.

Fact-file: Rebecca Long-Bailey Age: 37 Birth: Stretford, Trafford Education: Chester Catholic High School University: Manchester Metropolitan Career: Solicitor Seat: Salford and Eccles Current position: Shadow business secretary

"Now you have also said that your fiscal credibility rule means that you won't borrow to do any of this. So my questions to you is very straightforward, where does the money come from?"

Long-Bailey replied: "Well, we certainly wouldn't have made the decisions that this government has made, for example slashing the taxes for the most wealthy in society, inheritance tax, capital gains tax, the bank levy, corporation tax."

Marr: "So you'd reverse those. Let's talk about corporation tax, how much do you raise by reversing corporation tax?"

Long-Bailey: "Well, as a total package, we asked the House of Commons to do some research into the money that we would gain back by reversing all of those tax breaks, and its £70bn in total by 2020."

The self-styled socialist has been described as a "rising star", which is somewhat of an understatement. The former solicitor, 37, was only elected to the House of Commons in May 2015, when she succeeded ex-Communities Secretary Hazel Blears to become the next Labour MP for the Greater Manchester seat of Salford and Eccles.

Long-Bailey increased Blears' majority by more than 6,800 votes, leaving Conservative candidate Greg Downes in her wake.

Since the general election, Long-Bailey has been made shadow Treasury minister, shadow chief secretary to the Treasury and, as of last week, she was promoted to the shadow business secretary brief after fellow Jeremy Corbyn ally Clive Lewis quit the front bench to vote against the Article 50 bill.

The mother-of-one is on the fast-track to the top of the Labour Party and, crucially, she has the backing of fellow left-winger John McDonnell, the shadow chancellor.

"Rebecca Long-Bailey was brilliant on [BBC Question Time] with convincing common-sense answers. Next generation of our socialist leadership team emerging," McDonnell enthusiastically tweeted following Long-Bailey's appearance on the flagship debate show.

The shadow business secretary has some serious socialist credentials, with her Irish father, Jimmy, working on the Salford Docks and becoming a trade union representative in later life.

But what may be well less known is Long-Bailey's career as "high-flying solicitor", as the Manchester Evening News put it. She last worked for Hill Dickinson, specialising in NHS contracts and commercial property, according to her LinkedIn profile.

"Over the years I have held many jobs; working in shops, call centres and a furniture factory," Long-Bailey told the paper, playing down her professional background.

She was back in the news this weekend when The Sunday Times claimed, to denials from Labour, that it had polled the popularity of Long-Bailey, Shadow Education Secretary Angela Rayner and other left-wing frontbenchers.

The focus group research in Manchester, which Labour described as routine, reportedly saw Long-Bailey score highly, with respondents describing her as "passionate", "genuine" and "sincere". Surely good qualities to have in a Labour leader?