The British economy grew at the fastest pace in nearly a decade in the second quarter, higher than initially estimated, thanks to a pick-up in the construction industry and strong household spending.

The Office for National Statistics' second estimate for the second quarter showed GDP rose 1.2% between April and June, the fastest growth since the first quarter of 2001. The figure was unexpectedly revised higher from the initial estimate of 1.1% released a month ago and compared with 0.3% growth in the first three months of the year.

Economists, however, cautioned that the conditions that fuelled growth over the past three months will not continue, with firms that were building up their inventories slowing consumption and consumers likely to hold off spending as the government's austerity measures start to bite and VAT is hiked in the new year.

"The rebound in manufacturing we've seen over the past nine months appears to be feeding into tentative signs of a recovery in investment which, if continued, should deliver the much-needed rebalancing of the economy," said Lee Hopley, chief economist at the manufacturers' organisation EEF. "However, the strong bounce in overall growth remains reliant on consumer spending and restocking, both of which are likely to diminish in the second half of the year, placing greater importance on investment and a pick-up in trade."

Hetal Mehta, UK economist at Daiwa Capital Markets Europe, warned the quarter was likely "to represent the high point of quarterly growth as fiscal tightening and a renewed slowdown in global activity constrains a more robust recovery".

The figures showed construction output proved stronger than first thought, soaring by 8.5%, the highest rate since 1982. Consumer spending rose by 0.7%, compared with a 0.1% drop in the first quarter, the strongest quarterly rise since early 2008. Government spending advanced by 0.3%.

The figures also showed that a large contribution to growth came from companies rebuilding stock levels, which were up £1bn – the first positive outturn since the autumn of 2008.

Britain's service industries expanded by 0.7%, with business services and finance bouncing back with 1.5% growth, while manufacturing moved 1.6% ahead.

Retail sales have held up surprisingly well, according to the Confederation of British Industry's August survey published on Thursday, suggesting that momentum continued into the early part of the third quarter.

The GDP figures will allay some fears of a double-dip recession, but economists are concerned growth could slow again.

A Treasury spokesman said: "While the government is cautiously optimistic about the path for the economy, the job is not yet done. The priority remains to implement the budget policies which support economic rebalancing and help ensure the sustained growth that the Office for Budget Responsibility forecast this year and next."

Economists noted that investment posted a 2.4% drop in the second quarter, including a 1.6% drop in business investment, and trade made no contribution to economic growth.

"Government spending is going to move into negative territory while net trade could suffer if global growth concerns, following softer US and Asian data, materialise," said James Knightley at ING. "This places a heavy burden of growth on investment. Consequently, we continue to believe GDP growth will average around 1.5%-2% over the next three years or so."

Samuel Tombs at Capital Economics added: "The recovery is built on very fragile foundations. Household and government spending did both post solid rises, but both sectors are very unlikely to maintain such growth rates as the fiscal squeeze kicks in over the coming quarters.

"With increasing evidence that the global recovery is faltering, the external sector still looks unlikely to push the economy strongly forward over the next year or two."