Lukewarm demand for about 5.75 billion pounds of London offices on the market will likely force sellers to cut prices up to 15 percent, bringing them back to more realistic levels, property experts told Reuters.

So far, offers are believed to have been made for about 1.7 billion pounds of the offices, which are in London's City financial zone and Canary Wharf business hub, global real estate consultancy CBRE said. It is not clear how many are under offer.

Realistic pricing remains the key if the 'under offer' is to become a 'sold', CBRE executive director Mike Edwards said, noting the dearth of big deals in the last quarter of 2011.

The total level of transactions is being restrained by some unrealistic asking prices. If these were to ease, total investment turnover would increase, Edwards said.

A series of high-profile City office properties came to market in the autumn months as their owners looked to capitalise on prices that the IPD benchmark said rose 34 percent between June 2009 and September 2011, fuelled by demand from cash rich overseas investors looking for a safe haven investment.

Sellers also sought to cash in before a potential downwards lurch in the UK economy as a result of the euro zone sovereign debt crisis.

On Wednesday, a Reuters poll of more than 40 economists found there was a 50 percent chance the UK economy could slip back into recession within a year, but that it was unlikely to leave the 27-nation European Union.

UK commercial property values fell for the first time in almost two and a half years in November, IPD said on Wednesday, possibly signalling an inflection point in the country's commercial propert market.

The U.S. debt downgrade in August shook people as they couldn't see where rental growth would come from, said Franco Sidoli, co-founder of broker Franc Warwick. The trouble was it was a herd instinct and everyone thought it at the same time.

Larger deals included a billion pound portfolio of four properties being sold by German fund Kanam, including Deutsche bank's London base. Goldman Sachs' Peterborough Court UK home is up for sale, as is a 300 million pounds-plus building housing Credit Suisse in Canary Wharf.

SKYSCRAPER PRICES

Other prime offices on the block are the iconic Tower 42 skyscraper, which is close to being bought by South African investor Nathan Kirsh, and Drapers Gardens, a building that houses asset manager Blackrock and on the market for a reported 280 million pounds.

The Drapers Gardens price was described as punchy by one source close to the deal who said they would be very surprised if it was achieved.

A lot has gone under offer but the pricing has not yet been revealed, Sidoli told Reuters. The trend is downwards and I'd estimate an average discount to the asking price of between 10 and 15 percent.

Prices would likely fall as the result of weakening rental growth said John Cahill, a property analyst at Evolution Securities. Looking around at the large empty buildings in the City I think it's reasonable to assume we'll see downward pressure on capital values, he told Reuters.

Wealth manager Schroders shelved a deal to move into the Walbrook building near the Bank of England at the eleventh-hour recently due to the uncertain economic outlook.

Five central London skyscrapers being developed by firms including Land Securities and British Land have only signed one office pre-let deal between them.

Prices for top-drawer assets would likely hold firm on the back of global demand said Nick Braybrook, a partner at real estate firm Knight Frank, citing the 176 million pound sale of a building by Hammerson on Thursday to the real estate arm of Kuwait.

Of the stock on the market, the good assets in great locations still work very well for international investors looking to put their money into London. Prices elsewhere could come down, he said.

It is more complex and takes twice as long to convert an offer into a sale because of the jitters in the financial markets, Sidoli said.

The due diligence is forensic. Big deals that took three weeks now take about six, he said.

(Reporting by Tom Bill; Editing by Andrew Macdonald)