Economists polled by Reuters had expected growth of 4.6 per cent in August, according to the median forecast.
The increase represented the fourth consecutive month of growth but was only marginally above the lowest of the 27 forecasts in the Reuters poll.
The economy – which shrank by more than any other Group of Seven nation in the April to June period – remained 9.2 per cent smaller than its level just before the pandemic hit Britain, the Office for National Statistics said.
“The economy continued to recover in August but by less than in recent months,” said ONS deputy national statistician for economic statistics Jonathan Athow.
The dominant services sector grew by 2.4 per cent from July, a lot slower than expectations for growth of 5 per cent.
Growth in the smaller manufacturing and construction sectors also fell short of forecasts.
Economists have warned that the British economy may struggle to grow in the months ahead as the number of COVID-19 cases began to rise in September and the government responded by tightening its restrictions on people gathering together.