Cadbury has reduced the size of Dairy Milk sharing bars by 10% as it passed on the impact of soaring costs to customers.
Parent company Mondelez blamed rising inflation in the production of its chocolate as it reduced the size of its larger bars from 200g to 180g.
The bars are still being typically sold at £2 despite the size reduction.
US parent company Mondelez said the shrinkflation - reducing the size of a product but keeping its price the same in order to improve profitability - was the first by Dairy Milk in a decade.
In 2012, a 49g bar was reduced to 45g but the price remained 59p.
Meanwhile, a year earlier the 140g chocolate bar was reduced in size to 120g.
It comes as the cost of living crisis gathers pace, with accelerating food inflation placing pressure on UK households.
Last week, Consumer Price Index (CPI) inflation struck a new 30-year-high of 6.2% for February and is expected to soar beyond 8% in the coming months.
The figures for February showed that food inflation increased by 5.3% year-on-year, with milk, fresh meat and coffee reporting particular sharp increases.
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A Mondelez spokesman said: "We're facing the same challenges that so many other food companies have already reported when it comes to significantly increased production costs - whether it's ingredients, energy or packaging - and rising inflation.
"This means that our products are much more expensive to make.
"We understand that consumers are faced with rising costs too, which is why we look to absorb costs wherever we can, but, in this difficult environment, we've had to make the decision to slightly reduce the weight of our medium Cadbury Dairy Milk bars for the first time since 2012, so that we can keep them competitive and ensure the great taste and quality our fans enjoy."
A report earlier this year found nine in 10 Brits are furious about the curse of 'shrinkflation' - where their favourite products have shrunk for the same price.
A study of 2,000 adults found 87 per cent feel products they buy seem smaller than they were years ago, with 83 per cent noticing the difference in their favourite chocolates the most.
As many as four in 10 adults are outraged at the reduction of a Quality Street tin by as many as 550 grams over the years.
While 36 per cent are upset that standard Mars Bars are 11.5 grams less than they were in the eighties.
Shoppers are also horrified to buy boxes of Jaffa Cakes only to find 10 in the box instead of 12, and Andrex toilet tissues which are 21 sheets fewer per roll.
And with Easter weekend looming, 29 per cent still can't get over the fact there are only five Cadbury's Creme Eggs in a box, instead of six.
The poll found one quarter of adults feel they no longer get value for money for their Terry’s Chocolate Orange, which reduced in size from 175 grams to 157 grams.
While 37 per cent have done a double take when opening up their tin of Roses, and one fifth have been disappointed with the 20 grams reduction on their Doritos sharing bag.
Other products which Brits have been saddened to see shrink include Birds Eye Fish fingers, Maltesers, Sensodyne toothpaste and Philadelphia.
And shoppers say they are always most disappointed to realise their chocolate has been downsized (55 per cent), followed by crisps (44 per cent) and toilet rolls (38 per cent).
One third of Brits has stopped buying a product altogether in protest of Shrinkflation, and seven in 10 admit they would stay more loyal to a brand that maintained its product sizes despite rival brands opting to go smaller.
PRODUCTS BRITS ARE MOST SAD ABOUT SHRINKAGE
- Quality Street – weighed 1200g in 2009 now 650g
- Tin of Roses – weighed 1100g in 2009 now 600g
- Mars Bar – reduced from 62.5g to 58g then to 51g
- Bag of Maltesers – shrunk from 121g to 93g
- Crème Egg – pack of 5 instead of 6
- Jaffa cakes – packet cut by 12 to 10
- Cadbury Heroes tub – gone from 660g to 600g
- Cadbury’s multipacks – bars reduced so all are under 200 calories
- Toblerone bar – reduced bar size from 400g to 360g
- Terry’s Chocolate Orange – reduced from 175g to 157g
- Birds Eye fishfingers – cut pack from 12 to 10
- Dorito’s sharing bag – reduced from 200g to 180g
- Cadbury’s mini rolls – sold in packs of 10 not 12
- Andrex toilet rolls – reduced each roll by 21 sheets
- Aero mint – reduced from 120g to 100g
- M&Ms family bag – shrunk from 165g to 140g
- Sensodyne Toothpaste – 100ml to 75ml
- Philadelphia – shrank from 200g to 180g
- Hovis bread – 800g to 750g
- Box of PG teabags – reduced from 250g to 232g
- Tetley Teabags – sold in packs of 88 not 100
- Coco Pops – large box reduced from 800g to 720g, small 550g to 510g
- Tropicana juice – reduced from 1.75L to 1.6L
- Surf washing powder – does 23 washes instead of 25
- Colman’s tartare sauce – reduced from 250ml to 150ml
