Christmas dinner with all the trimmings could lead to congealed cooking oil and grease blocking drains up and down the country, water companies have warned.

Engineers from Severn Trent Water have been digging tons of fatty gunk, which sets as hard as concrete, out of sewers in the West Midlands after reports of flooding caused by fatbergs.

With Christmas approaching, the company is urging its 3.7 million customers to think twice before tipping hot oil down the drain, to avoid an increase in blockages.

Water companies are warning of a buildup of blocked drains after households have prepared roast potatoes, buttered greens, basted birds and pigs in blankets for traditional Christmas dinners.

Severn Trent is offering households free “gunk pots” on its website, in which grease can be stored until cool and then put in the bin.

Yorkshire Water said it was looking to help tackle festive fatbergs with its fat vat scheme, launched in Bradford in 2014, which instead allows residents to collect unwanted oil for use as biofuel.

The scheme, run with the Karmand community centre, has collected 3,000 litres of oil from 268 households. There are plans to expand the scheme throughout the Bradford Moor district, covering up to 6,000 homes.

Duncan Woodhead from Yorkshire Water said the project was aimed at changing the behaviour of residents who had been unaware of the risk of fatberg blockages.

“The local community in Bradford have really bought into the scheme and since it launched in 2014, there has been only one sewer blockage due to fats, oils and greases, compared with 85 blockages between 2011 and 2014,” he said.

Meanwhile, Severn Trent said work to dig out a blockage in Fairfax Street, Coventry, was continuing after several floodings were reported in the area in recent months.

Fat, oil and grease cause more than three-quarters of the tens of thousands of blocked drains the company has to deal with every year.

Severn Trent said its engineers were also preparing for callouts during the festive period to remove more unusual items, which in previous years have included a motorbike, a pair of novelty Muppets slippers and underwear.

James Jesic, an operations manager for Severn Trent, said: “Everyone loves to indulge at Christmas time and you may find your kitchen turning into a factory, churning out endless festive snacks and treats, but please don’t pour hot fat and grease down the sink.

“It might seem harmless when you’re doing it, but that grease quickly solidifies when it cools and sticks to the sides of our sewers, forming a concrete-like solid that attracts other debris, eventually causing a blockage.

“With no way through, the waste water backs up the system, coming out of drains and sewers in roads or even into homes. Nobody wants a flooded house for Christmas.”

Yorkshire Water said 110,000 tonnes of used cooking oil is disposed of each year by UK households, which could power 110,000 homes with carbon-neutral electricity.