* 7 percent jobless rate set as threshold for action
* Economy recovering but slowly, Carney says
* Not worried by rally in house prices
* Markets gyrate, noting caveats to forward guidance
By David Milliken and Olesya Dmitracova
LONDON, Aug 7 (Reuters) - The Bank of England overhauled its policy strategy on Wednesday, saying it planned to keep interest rates at a record low until unemployment falls to 7 percent or below, something unlikely for another three years.
Barely a month after Canadian Mark Carney took over as governor, the central bank said it would keep interest rates at 0.5 percent unless inflation threatened to get out of control or there was a danger to financial stability.
Carney said a recovery in Britain's fragile economy was underway and it appeared to be broadening but he warned that it had a long way to go before it was on solid ground.
"This remains the slowest recovery in output on record," he told his first news conference since taking over at the Bank. "We're not at escape velocity right now."
The pound rallied after an initial fall on the announcement and British government bond prices were lower as the BoE's commitment on interest rates fell short of some expectations of a more aggressive plan to revive growth.
"It looks like rates are not going to rise in the next three years, though they could, as Carney has stressed they are not pre-committed, so again this is a rather valueless bit of 'forward guidance' as is the case with the ECB," said Mark Ostwald at Monument Securities.
The Bank of England followed the U.S. Federal Reserve's approach by setting an unemployment target rather than committing to keeping rates low for a set period of time but included get-out clauses.
BoE policymakers said they stood ready to buy more government bonds if additional stimulus was needed and would not reverse existing purchases while unemployment was too high.
The central bank said inflation was forecast to stay above its 2 percent target until the second half of 2015 based on market rate expectations.
"Attempting to return inflation to the target too quickly risks prolonging the period over which the nation's resources are underutilised," it said.
A growing number of major central banks are providing so-called forward guidance to help nurse their economies back to health after the damage of the financial crisis.
For the BoE, the challenge is to hold off a premature rise in British borrowing costs at a time when signs of economic recovery at home and the U.S. Federal Reserve's decision to phase out stimulus are pushing up market interest rates.
Last month its Monetary Policy Committee took a step towards guidance by saying that a rise in British market rates was not justified by economic fundamentals, and it reiterated that point on Wednesday.
Markets already did not expect the BoE to start to raise interest rates until late 2015 at the earliest.
THREE YEARS' GRACE?
The BoE said Britain's economy had strengthened over the past three months. But output still remains more than 3 percent below its pre-crisis peak, a much weaker recovery than in the United States or Germany.
It now forecasts the economy will grow 0.6 percent during the current quarter - the same as between April and June, and that growth will reach an annual rate of 2.6 percent in two years' time, compared with 2.2 percent forecast three months ago, assuming interest rates stay on hold.
Unemployment is forecast to fall only slowly from its current level of 7.8 percent of the workforce, with the central bank expecting it to average 7.1 percent in the third quarter of 2016, the end of its forecast horizon.
This implies that the BoE expects to keep interest rates unchanged until at least that time, unless one of three conditions is breached before then.
The BoE will consider raising interest rates if their low level poses a threat to financial stability, if the public's medium-term inflation expectations rise dangerously high or if it forecasts that inflation in 18-24 months will be at 2.5 percent or higher.
It said that if those thresholds or the 7 percent unemployment rate are reached, the MPC would consider the case for interest rate rises on a month-by-month basis.
"There is therefore no presumption that breaching any of these knockouts would lead to an immediate increase in Bank Rate or sale of assets," it said.
Inflation is forecast to average 2.9 percent in the last three months of this year - close to its current level and a lower peak than previously thought - and then to fall roughly as predicted three months ago.
Finance minister George Osborne named Carney in November to succeed King, impressed by the Canadian's reputation for innovative thinking and applying forward guidance while he led Canada's central bank.
Osborne welcomed the plan and said it was consistent with the government's "absolute commitment" to Britain's 2 percent inflation target.
Carney has previously stressed the importance of reassuring ordinary people and businesses that their debt costs are not going to rise any time soon in order to give them more confidence about spending which would help the economy.
The new governor also signalled he was not concerned about signs of a fast recovery in the housing market in some parts of Britain, especially London.
"The housing market is starting to recover and actually the overall level of housing activity relative to GDP is a couple of percentage points lower than where it was prior to the crisis," Carney said at the news conference.