LONDON--Consumer confidence edged up in the U.K. in August, driven by the fast improvement of the economy during the last year, research firm GfK said Friday.

GfK's consumer confidence index increased to +1 in August from -2 in July, as respondents expressed positive views about the economy and their personal financial situation. The increase was higher than economists had forecast.

Confidence from consumers is yet another sign that the British economy is set to have a strong third quarter of the year, after higher expectations for household consumption led the British Chambers of Commerce to upgrade Thursday its gross domestic product growth forecast for the year to 3.2% from 3.1%.

The index has remained more or less stable for the last three months after a sharp boost in the first quarter, reflecting a faster-than-expected expansion of GDP and tumbling unemployment.

GfK said the improvement in consumer confidence largely reflects a reassessment of the recent past by households, although people are also increasingly optimistic about the future.

"There is no guarantee how long this stable position will last--a rush of good or bad economic news could set off a marked rise or fall--but things could stay like this for a while," said Nick Moon, managing director of social research at GfK.

The survey also registered an increase in the consumers" will to both save and make major purchases, such as furniture or electrical goods. These results are consistent with the recent Confederation of British Industry Distributive Trades Survey, which showed a great majority of businesses reporting higher sales volumes, with furniture retailers ranking on top.

The GfK survey, which uses figures that aren't seasonally adjusted, polled a sample of 2,000 individuals aged 16 or more.

Write to Jon Sindreu at jon.sindreu@wsj.com

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