Detailed Instructions: In this task, you are given an article. Your task is to summarize the article in a sentence.
Problem:Chancellor George Osborne has fought moves to introduce such a tax, warning it would harm the City.
The Labour Party has also been against a Financial Transaction Tax (FTT).
But Mr McDonnell believes it could rein in the excesses of the financial sector and help pay for improvements to the NHS and other public services.
He told a fringe meeting at the Labour conference in Brighton that he had reached an agreement with Shadow Business Secretary Angela Eagle to launch an "open" debate in Labour with a view to making a Financial Transaction Tax party policy.
He told the Unite meeting that his conference speech on Monday "won't be one of my normal rants" and "might be stultifyingly boring" because he would be setting out a series of "economic initiatives" Labour had planned.
He has long campaigned for a Financial Transaction Tax and revealed that he had a furious row with his predecessor as shadow chancellor, Ed Balls, when he tried to secure a Commons debate on the issue.
David Hillman, of the Robin Hood Tax campaign, which has gathered more than a million signatures on its petition, told the meeting there was nothing "dangerous or radical" about the idea, which he said had support from across the political spectrum in Europe.
The point of the tax, which would be levied on stock and foreign exchange trades, would be "to have the banks and hedge funds pay for, or at least contribute to paying for, the immense economic damage their gambling, essentially it was gambling, had caused," he said.
Mr McDonnell said he would use his speech to "demand" access to the financial models used by the Office for Budget Responsibility and the Bank of England to help Labour formulate an alternative economic policy and calculate the rate at which a Robin Hood tax could be set.
"I think that should be open to all parties in Parliament" to test their own ideas "in advance of getting into government," he added.
He will also announce a review of Her Majesty's Revenue and Customs to find out how it could beef up its efforts to collect the billions of pounds avoided by UK companies and individuals every year.
Mr McDonnell said he wanted to examine every aspect of HMRC, "its operations, effectiveness and also look at its range of policies and the instruments that it has available to it to ensure that we maximise our tax take and at the same time it's done on a fair and just basis".
During his Labour leadership campaign, Jeremy Corbyn claimed Â£120bn could be recovered from tax avoidance and evasion - enough to pay off the deficit without cutting welfare or public spending.
But critics, including the then shadow chancellor Chris Leslie, said it was not a plausible policy and would not work.
Solution:
John McDonnell looks set to use his first Labour conference speech as shadow chancellor to push for a "Robin Hood" tax on stock market trading.