The Bank of England's chief economist, Andy Haldane, is ready to vote for an increase in UK interest rates "relatively soon".
The news is likely to come as a surprise to financial markets because Mr Haldane has long been considered to lie on the more dovish end of the Monetary Policy Commitee's spectrum.
Sterling spiked to $1.2684 in response, up 0.42 per cent on the day.
The MPC is at its most split on interest rates since 2011.
Last week three members of the committee - Kristin Forbes, Michael Saunders and Ian McCafferty - voted to increase rates from 0.25 per cent to 0.5 per cent, while the other five, including the Bank's Governor Mark Carney, voted against.
In a speech in Bradford on Wednesday Mr Haldane revealed he is likely to join them in "the second half of the year".
"Having weighed the evidence, I think that the balance of risks associated with tightening 'too early', on the one hand, and 'too late', on the other, has swung materially towards the latter in the past six to nine months," he said, citing stronger global growth and a dissipation of market fears of deflation.
"A partial withdrawal of the additional policy insurance the MPC put in place last year would be prudent relatively soon, provided the data come in broadly as expected in the period ahead. Certainly, I think such a tightening is likely to be needed well ahead of current market expectations."
Mr Haldane's views are also significant because he, unlike the three other MPC members who are in favour of the rate rise, is a member of the Bank's permanent staff, rather than an external member.
On paper Mr Haldane's switch opens the prospect of a 4-4 split on the MPC at its next meeting in August.
The MPC normally has a nine members but the deputy governor Charlotte Hogg resigned earlier this year and is yet to be replaced.
Under a deadlock the Governor would have the casting vote.
However, Ms Forbes leaves the MPC at the end of this month and will be replaced by Silvana Tenreyro.
And at the Mansion House on Tuesday, Mr Carney struck a different note from Mr Haldane, saying "now is not yet the time" to begin tightening monetary policy.
Mr Haldane has reversed himself on his position on rate rises before. In June 2014 he gave a speech in which he suggested he favoured a "front foot" move to increase rates, only to change his mind later in the year when the data became "gloomier".
Mr Haldane stressed that raising interest rates to 0.5 per cent "would still leave monetary policy highly accommodative by any historical metric" and given the Bank's money printing since last August it would still be looser than before the Brexit vote.
He said that the risk of tightening too late was that it could force the Bank to hike rates much more rapidly to stem rising inflation, which hit 2.9 per cent in May, reflecting the slump in sterling since last June's referendum result.
"Provided the data are still on track, I do think that beginning the process of withdrawing some of the incremental stimulus provided last August would be prudent moving into the second half of the year," he said,
Mr Haldane joined the MPC in June 2014 and voted along with the rest of the MPC to cut rates to 0.25 per cent last August. He also voted at that point to increase the Bank's money printing programme.
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