P.M. BRIEFING : British Inflation Over 10% Mark

LONDON —  Britain said today that its annual inflation rate broke through the psychologically important 10% level in August for the first time in eight years.

The retail price index, the country’s main measure of inflation, showed a year-on-year rise of 10.6% last month, up from 9.8% in both June and July.

It was higher than financial analysts had expected, but the London stock and currency markets took it in their stride and were little changed by the news.

The underlying inflation level, which excludes home loans and local taxes and is seen by some economists as a more accurate measure of price increases, also rose from 7% in July to 7.9% in August.