Hundreds of millions of pounds have been wiped off the value of Britain's largest shopping centres over the past year and the writedowns are set to continue, one of the UK's biggest retail property owners said yesterday.

The warning from Liberty International, the owner of Lakeside in Essex and Covent Garden in Central; London, came as it announced a £345 million writedown to the value of its £8.34 billion retail holdings during its first three months' trading this year.

Values of regional high street shops and older retail parks came under pressure a year ago before the onset of the credit crunch, as fears grew that many highly leveraged investors had overpaid for assets where there was little prospect of rental growth.

However, first-quarter figures published yesterday by Liberty show that the declines in values of prime retail property have also been hard hit since the autumn.

Liberty has taken more than £600 million of writedowns to the value of its holdings between October 31 and March 31.

Lakeside's value declined by £53 million over the first quarter of the year to £1.19 billion. In March 2007 it was valued at £1.32 billion.

Covent Garden's value has fallen by about £25 million over the past year to £649.4 million. Liberty bought the piazza in August 2006 for £421 million and has bought adjoining sites since then.

David Fischel, Liberty's chief executive, said: “We are probably back [in values] to where we were two years ago.”

The downward trend experienced by Liberty makes it likely that British Land, one of the country's other big owners of retail property, will mark down the value of its Meadowhall shopping centre in Sheffield by up to £75 million for its full-year figures to the end of March. Meadowhall was valued at £1.64 billion at the start of 2007 but by the end of the year British Land had shaved its value by £140 million.

The declines in shopping centre values have been a direct result of the credit crunch, while the withdrawal of cheap debt from the investor market has increased yields - the rental return as a proportion of price paid. Moreover, the squeeze on credit shows no sign of letting up and there are increasing concerns that rents, even at well-let companies such as Liberty, will come under pressure as shops struggle to deal with the rapid decline in consumer confidence.

That, in turn, could lead to another decline in retail property values, Mr Fischel said. “Further upward movement in valuation yields [declining prices] may well be experienced in 2008 as investment property remains unsettled in the light of ongoing uncertainty in financial markets and the general tightening of credit conditions. In particular, rental levels are likely in the next few years to become an increasingly important factor in valuation performance.”

Liberty has 98.5 per cent of its shops let, a mere 0.2 per cent decline on its occupancy rates from a year ago.

Malcolm Dalgleish, European head of retail at CB Richard Ellis, told The Times: “Landlords are now considering requests from existing tenants to be flexible on rental and general tenancy terms if they perceive shops to be running into genuine trading difficulties. This is a particular problem in weaker shopping centres.”

Mr Fischel said that he had not yet seen any increase in tenant requests, but added: “It is possible that tenants are asking for more - it is in our interests to keep centres full. We look at individual requests on a case-by-case basis. We don't like units coming back, as we do not want to re-let; it is better for them to keep in business.”

Jeremy Helsby, chief executive of Savills, the property agency, said that prices of secondary retail property outside London could fall up to another 10 per cent this year.

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