Boris Johnson's roadmap for exiting lockdown has kickstarted a mini economic boom as businesses hire staff and order stock ahead of reopening.
IHS Markit's closely watched private sector survey found the UK economy was performing better than expected thanks to a surge of optimism and preparations for the grand unlocking.
IHS Markit's latest purchasing managers' index (PMIs), published on Wednesday, recorded a 'flash' reading of 56.6 in March. It marked a seven-month high for the index, powered by the fastest growth in the UK's services sector since August and a 40-month high for manufacturing activity.
PMIs are given on a scale of 0 to 100. Anything above 50 signals growth, while below marks contraction. Economists had expected Wednesday's 'flash' estimate to come in closer to the 50 mark.
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"The UK economy rebounded from two months of decline in March, with business activity growing at its fastest rate since last August as children returned to schools, businesses prepared for the reopening of the economy and the vaccine roll-out boosted confidence," said Chris Williamson, chief business economist at IHS Markit.
"Companies reported an influx of new orders on a scale exceeded only once in almost four years, and business expectations for growth in the year ahead surged to the highest since comparable data were first available in 2012."
Booming business was "linked to the prospect of looser restrictions," IHS Markit said. The prime minister set out the UK's roadmap out of lockdown at the end of February, giving businesses a clear indication of how and when to prepare.
IHS Markit recorded the first increase in private sector employment since the pandemic began in March, as businesses hired staff ahead of the grand reopening.
Williamson said the findings "hints at only a modest contraction of GDP during the first quarter."
James Smith, an economist at ING, said the survey showed "green shoots" in the UK economy and signs that some of the Brexit-driven disruption to trade was beginning to ease.
"Sharply higher growth numbers are on their way," Smith said. "We expect growth of around 2% in March, albeit mainly linked to school reopenings. For the second quarter as a whole, we reckon growth will come in at 4-5%, after a circa 2% decline in the first quarter."
Williamson cautioned that "worries persist." Exports remain depressed and some companies still face supply chain issues.
"Many consumer facing companies meanwhile remain constrained by COVID-19 restrictions, which are likely to curb the overall pace of economic growth for some time to come, especially if we see a third wave of infections," he said.
Data for the eurozone, published by IHS Markit earlier on Wednesday, showed Europe's economy was also performing better than expected. March's flash reading was 52.5, compared with expectations of 49.1.