LONDON (Bloomberg) — Internet advertising spending in the UK rose 17 percent last year, while total ad expenditure declined amid the economic slump.

UK internet spending totalled £3.35 billion ($4.8 billion) in 2008, the Internet Advertising Bureau reported yesterday in its bi-annual ad spending report. Total expenditure fell 3.5 percent to £17.5 billion.

Britain is now the most developed market for internet advertising, accounting for 19.2 percent of overall spending. Online advertising topped the share of placements in newspapers and magazines, the bureau said.

"These are really tough times and advertising budgets are being slashed," IAB chief executive officer Guy Phillipson said in a press release announcing the report. "More than ever, marketers have to demonstrate a clear return on their media investment - and accountability is online's trump card."

Paid-for search ads grew the most among online placements to almost £2 billion, as advertisers sought "guaranteed accountability, measurability and fast results", the bureau said.

The report was carried out in conjunction with PricewaterhouseCoopers LLP and the World Advertising Research Centre.