On the year, retail sales were up 3.9 per cent last month, also a four-month high, helped in part by a weak performance in the same month last year. Some economists had expected a rise of 4.1 per cent.
Consumers have been the main driver of the country’s economic recovery which began last year, helped by record low interest rates and weak inflation that has eased the pressure on their spending power.
Wage growth, however, remains weak - something the Bank of England has put at the centre of its debate on when to start weaning Britain off record-low interest rates.
Prices in stores fell 1.2 per cent in August, the steepest decline in more than five years, as prices in petrol stations fell 5 per cent. Prices in food stores showed their first annual fall since 2004 as supermarkets waged a price war.
The ONS said sales of furniture soared 23.4 per cent year-on-year, helped by sales of desks and flat-pack furniture for students ahead of the start of the academic year.
An ONS official also a pointed a surge in sales of high-powered vacuum cleaners, as shoppers sought to beat an end-of-August introduction of European Union rules to ban the sale of high-powered appliances.
Similar bans are planned early next year for hairdryers, lawnmowers and electric kettle as the EU tries to curb energy use and greenhouse gas emissions, said the ONS official.
Retail sales account for just under 6 per cent of gross domestic product.