* BoE's Vlieghe says wage pressure building gently
* Slack in economy diminishing - Vlieghe
* Vlieghe considered MPC member most supportive of low rates
* Sterling jumps again
* Two- and five-year gilt yields hit post-Brexit high (Recasts, adds details throughout)
LONDON, Sept 15 (Reuters) - The prospect of British interest rates rising for the first time in 10 years grew on Friday when a Bank of England policymaker who had been its strongest advocate of ultra-low borrowing costs said rates might need to rise in the coming months.
The comments by Gertjan Vlieghe largely echoed the BoE's message a day earlier, when it surprised investors by suggesting it could raise rates as soon as at its next meeting, in November.
But coming from Vlieghe, they prompted investors to pile on bets on a rate hike, despite several false starts in recent years when the BoE has previously hinted at changes in policy only to be overtaken by changes in the economy.
Vlieghe was the first MPC member to vote for a rate cut after Britain's shock referendum decision in June 2016 to leave the European Union. In July this year, he said a premature hike would be a bigger mistake than one that was slightly late.
After his speech on Friday, sterling hit its highest level against the U.S. dollar since the Brexit vote, peaking at $1.3616.
"Its been quite an incredible week for the pound, with the currency soaring across the board," David Cheetham, chief market analyst at XTB online trading said. "An increase at the next meeting in November is now odds-on according to the markets."
Yields on two- and five-year British government bonds, which are sensitive to short-term speculation about rates, also hit their highest level since the Brexit vote.
Ten-year gilt yields were set for their biggest one-week jump since June 2013, with a rise of 32 basis points.
Vlieghe said that until recently, he had favoured holding off on monetary policy changes, given Britain's slow economic growth and the lack of inflation pressures other than the impact of the Brexit fall in the pound.
"But the evolution of the data is increasingly suggesting that we are approaching the moment when Bank Rate may need to rise," he said.
"If these data trends of reducing slack, rising pay pressure, strengthening household spending and robust global growth continue, the appropriate time for a rise in Bank Rate might be as early as in the coming months."
Vlieghe said there was still a risk that Brexit hits the economy harder.
"If that happens, monetary policy would respond appropriately," he said. "But for now, it seems the net effect of the many underlying forces acting on the UK economy is that slack is continually being eroded and wage pressure is gently building."
Brexit represents a major challenge for the BoE.
The fall in the value of the pound since the referendum has propelled inflation to nearly 3 percent, above its 2 percent target. But economic growth remains weak and there still remains little sign of a strong pick-up in wages.
Vlieghe said that wage growth was not as weak as earlier in 2017 and that he expected it to pick up further.
Earlier this week, official data showed Britain's unemployment rate fell to a four-decade low of 4.3 percent while inflation rose to 2.9 percent, above the BoE's 2 percent target.
HAVE CAKE AND EAT IT?
Some economists remain unconvinced that the BoE really is on the verge of its first rate hike since 2007, especially given the emphatic 7-2 vote by Monetary Policy Committee members this week to keep Bank Rate at 0.25 percent.
Allan Monks, at JP Morgan, said it was possible that the BoE wanted to prepare financial markets for a hike, after its previous, subtler warnings fell on deaf ears.
"A second explanation for the BoEs policy inaction yesterday is that it still wants to have its cake and eat it i.e. effectively generate some degree of tightening without actually changing rates," he wrote in a note to clients.
Asked about the intensification of the BoE's message this week, Vlieghe said it represented part of a year-long evolution by the central bank. (Writing by William Schomberg; Editing by Hugh Lawson)