BoE faces tricky balancing act in Nov QE decision

* Analysts split whether BoE will raise or halt QE

* Diverging data may cloud decision

* Weak pound could raise inflation forecast

LONDON, Nov 5 (Reuters) - Bank of England policymakers face their toughest call in months on Thursday, when they must decide whether to inject more stimulus into the economy just as new data suggests Britain may be emerging from recession. Analysts are almost evenly split between the central bank topping up its 175 billion pound asset purchase programme by 25 billion pounds, 50 billion pounds, or calling an outright halt.

In fact, the only point they agree on is that interest rates will stay at 0.5 percent not just this month but well into next year as well.

"We believe the decision on QE is finely balanced and see the odds as 60:40 in favour of an extension versus the announcement of a halt," said Simon Hayes, economist at Barclays (LSE: BARC.L - news) Capital, who predicts a 50 billion pound top-up.

Until two weeks ago, most analysts had been expecting a small or no further expansion to the QE programme after a run of strong data suggested Britain had caught up with its main European neighbours and returned to growth in the third quarter.

Rebounding stock markets, rising house prices and an improvement in consumer morale reinforced expectations that conditions were starting to perk up.

But official data showing the economy in fact contracted by 0.4 percent in the period, marking Britain's longest recession on record, caused many analysts to reassess their view.

And this week's surprisingly robust manufacturing and services PMI surveys have injected even more uncertainty into today's Monetary Policy Committee decision, due at 1200 GMT.

"It is unclear what relative weights the MPC (A050540.KQ - news) will assign to these conflicting signals," Barcap's Hayes added.

PRICE PRESSURES?

Some reckon the central bank will want to taper off the asset purchases to safeguard a recovery and avoid distressing markets, and will opt for a 25 billion pound expansion.

"If the MPC has any doubts about growth -- and they may have some given GDP -- or any worries about gilt yields rising sharply, they might do that: a sort of gradual wind-down rather than a cliff-edge stop, said Michael Saunders, economist at Citi.

But much will also depend on the central bank's latest growth and inflation forecasts, published next week but which will inform policymakers' decision today.

Inflation is well below its two-percent target but has not subsided as quickly as policymakers may have expected, and minutes to October's MPC meeting showed they had differing views on how the inflation outlook had shifted.

And a fall in the pound on a trade-weighted basis since the last forecasts in August could be enough to raise the inflation forecast slightly, despite the amount of slack in the economy, lessening the likelihood of more stimulus, economists say.

"The big changes have really been the exchange rate and the fact that inflation is higher than expected. I don't think the demand background is vastly different," said Philip Shaw, economist at Investec (LSE: INVP.L - news) , who sees no QE expansion.

"But if the MPC's convinced it needs more QE, it'll do 50 billion."

(Editing by Ron Askew)