The chief executive of Experian, the world’s largest credit-checking group, has said that market conditions will continue to decline and warned of slowing sales growth for the company as banks cut back on lending.

Don Robert said: “I’ve been in this business a long time and this is as big of a market challenge as I’ve seen in the last couple of decades.”

He revealed a decline in Experian’s second-quarter revenue growth as lenders refuse new loans in an attempt to reduce their exposure to the sub-prime crisis in the United States.

Shares in the FTSE 100 company, which conducts consumer credit checks for banks, retailers and other companies, plummeted by almost 20 per cent at one stage, closing down 9.5 per cent at 429¾p. About £600 million was wiped off the value of the company.

Reporting its half-year results to September 30, Experian pointed to a 16 per cent increase in sales, to $1.9 billion (£930 million), and a 15 per cent increase in earnings before interest and tax to $454 million.

LowerMyBills, the group’s American home-loans price comparison website that is particularly exposed to the turmoil in the sub-prime mortgage market, suffered a significant fall in sales but remained profitable. Even with this sales downturn, the North American division as a whole managed to increase operating profits from $272 million to $290 million.

Operating profits from the UK and Ireland rose 7 per cent in dollar terms, to $126 million before discontinued activities.

But investors took fright at the group’s depressed outlook for second- half sales in its two biggest markets, Britain and the US. Before yesterday’s news, shares in the company had already lost almost a quarter of their value since the start of July.

Experian said that organic sales growth, excluding acquisitions, slowed to 5 per cent in the second quarter of Experian’s financial year, from 7 per cent in the first. It is expected to slow again in the third.

“The market environment in the US and the UK is tough, and is likely to get tougher,” Mr Robert said. “Our financial services clients have deferred their spending for capital projects and for marketing to new customers. We know this is temporary. But we don’t see the end of it just yet.”

Analysts were more upbeat. Kevin Lapwood, at Seymour Pierce, said that growth was still in line with expectations despite slowing. He has a hold recommendation on the stock.

Experian said that strong demand for its credit information services from credit card and car finance firms in Britain and the United States helped to drive growth. Its CreditExpert website in the UK and Consumer Direct in the US, which enable consumers to check their credit status directly, also proved popular. Strong performances from its Asia-Pacific and Latin American businesses, as well as cost controls, also helped it to offset tough trading in America and Britain.

Mr Robert said: “The balance and the diversity in our portfolio protects us, and allows us to continue to grow even in challenging markets. We’ve put in place a strategic framework to support continued global investment and growth, and we’ve taken significant steps in the first half of this year to become leaner and more efficient”.

Experian was part of GUS, which also owned the retailers Argos and Homebase. GUS was split in October 2006, with Experian and the Home Retail Group, which now owns Argos and Homebase, listing separately on the London Stock Exchange.

Experian proposed an interim dividend of 6.5 cents a share, up 18 per cent on the same period last year.

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