If you find yourself thinking that household groceries just don't go as far these days it may not be your imagination, an investigation has found.

Some of the most commonly-bought household groceries have shrunk in size, while the price has remained the same.

In some instances prices have actually risen, even though pack sizes have fallen, the study by Which? found.

Tetley Blend of Both tea dropped from 80 to 75 tea bags in a packet, for example. But even so, Sainsbury's increased the price from £2.55 to £2.75, Which? said.

Check out the differences: Packet sizes of some popular items have decreased recently, Which? found

Similarly Asda increased the price of Philadelphia Light Soft Cheese from £1.84 to £1.87 despite the pack shrinking by ten per cent from 200g to 180g.

Surf Essential Oils Powder Tropical Lily & Ylang Ylang remained priced at £5 in Ocado and Tesco despite shrinking from 25 washes (2kg) to 23 washes (1.61kg).

And at Asda, Morrisons and Sainsbury's, the prices of Birds Eye Select Mixed Vegetables and Hovis Best of Both bread remained the same despite shrinking.

The move by manufacturers is often used to effectively increase prices without shoppers necessarily noticing - essentially inflation by the back door.

The watchdog reported that the majority of manufacturers said it was retailers who ultimately set the prices of products.

That shrinking feeling: Packets of Birds Eye Select Mixed Vegetables and Aunt Bessie's Homestyle Chips have both reduced in size

But it pointed out that supermarkets were unlikely to drop prices unless the wholesale cost fell.

It said: 'Products are losing 50g here and a few centimetres there, which is all adding up to a more expensive shop without you knowing why.'

Which? executive director Richard Lloyd said: 'Shrinking products can be a sneaky way of putting up costs for consumers because pack sizes shrink but the prices don't.

Shrunk in the wash: Some packets of Surf and bottles of Cif and Domestos have also decreased, Which? found

'It's now time for action on dodgy pricing practices that stops people from easily comparing products to find the cheapest.'

However despite packet sizes shrinking in some instances, shoppers are benefiting from falling grocery prices across the board thanks to supermarket price wars.

Shoppers have saved £400million in the past 12 weeks alone thanks to the cost of groceries falling by another 1.6 per cent.

Reduction: Tetley teabag and Hovis Best of Both loaves have shrunk by six per cent

Retailers have been focusing on cutting prices on everyday items such as eggs, vegetables and milk, rather than offering more complicated multibuy deals.