Some of the most expensive commercial office buildings in London have been placed into administration as a property empire built by Simon Halabi, the Syrian-born billionaire, began to crumble.

The High Court has appointed Ernst & Young, the accountancy firm, as administrator for six properties worth £500 million in a move that will trigger a sell-off of the assets. The office blocks in administration are: Aviva Tower, in the City of London; JPMorgan’s offices at 60 Victoria Embankment; Millennium Bridge House; New Court, in Carey Street; Ludgate House, on Bankside; and Leadenhall Court, also in the City.

The move marks the latest stage in an unfolding drama that began with the properties sinking into negative equity against a £1.15 billion senior loan and most recently involved HM Revenue & Customs serving wind-up petitions to chase £4.8 million in unpaid tax. The tax liabilities arose after the Revenue revoked the borrower’s exemption from withholding tax under the non-resident landlords scheme. Last month it ordered the liquidation of the companies that own the properties.

The saga has been closely watched by commercial property investors, who hope that an eventual sale will provide them with rich pickings at the bottom of the market. Yesterday, CBRE, the property services adviser, which is acting for bondholders in the loan secured against the properties, said that the administration would lead to a sale.

It has three years to sell off any assets, but David Martin, of CBRE, said that in the present, more favourable market conditions, it might be the case that “now is as good a time as ever”.

CBRE had appointed Ernst & Young as receiver for these six buildings plus Samson House, also on Bankside, on September 25, in response to the Revenue’s wind-up petitions. The property consultancy took on the role of special servicer from Hatfield Phillips, the American company, last month.

However, even before the Revenue’s involvement, the portfolio, which includes nine properties, was the subject of scrutiny after it emerged in June that the loan, due to mature on October 23, would be impossible to refinance after a steep fall in the value of the buildings to £929 million. The White Tower loan secured against a total of nine properties in London was called in in July after the investor failed to rectify the breach.

The decision this week to appoint an administrator means that court hearings for the Revenue’s wind-up petitions that had been scheduled for today and next week will no longer take place, as CBRE said that the court was satisfied that administration would lead to a recovery of the monies owed.

Mr Halabi, who ranked fourteenth on The Sunday Times Rich List in 2007 with a net worth of £3 billion, is notoriously secretive about the structure of his family’s property investments. Mr Martin described the ownership structure behind the properties in administration as “Byzantine”.

The six buildings are owned by seven legal entities that were set up for the purpose of refinancing the loan in 2006, according to CBRE’s records.

Mr Halabi owns shares in 30 companies, including these seven entities, and also manages the assets they hold. He also owned the In & Out Club in Piccadilly, which is up for sale through Jones Lang LaSalle with a price tag of £250 million.

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