More than 2,500 products have shrunk in size over the past five years but prices have stayed the same, according to the Office for National Statistics (ONS).
The lion's share of the so-called "shrinkflation" phenomenon was found in food and drink, with Toblerone chocolate bars alone becoming 10% smaller.
While the move has had little impact on the headline rate of inflation, the change in packet size has triggered a 1.22 percentage points rise within the smaller sub-category of sugar, jam, syrups, chocolate and confectionery.
The statistics agency said chocolate manufacturers had pointed the finger at the rising cost of raw materials as the trigger for the drop in size.
However, the European import price of sugar sank to its lowest level on record in March this year, while cocoa prices have dropped sharply since the record highs seen in 2015, the ONS said.
It also brushed aside the idea of Brexit being a key factor behind the shrinking size of chocolate bars.
"Manufacturers' costs may also be rising because of the recent fall in the value of the pound - leading some commentators to attribute shrinkflation on the UK's decision to leave the European Union," the ONS said.
"But our analysis doesn't show a noticeable change following the referendum that would point towards a Brexit effect.
"Furthermore, others (including Which?) had been observing these shrinking pack sizes long before the EU referendum, and several manufacturers have denied that this is a major factor."