Fairy lights on Christmas trees could cause slower broadband speeds, regulator Ofcom has warned, as it launched a new app to test Wi-Fi in homes.
The watchdog estimated up to six million homes and offices could improve their broadband connection, saying wireless networks are often not set-up correctly or suffer "interference" from electronic goods including baby monitors and microwave ovens - and even festive fairy lights.
The free Wi-Fi Checker app, for smartphones and tablets, allows homeowners to test the quality of their internet signal and suggests ways to enhance it.
Ofcom also released research which found more than a quarter of homes in the UK have "superfast" broadband connection of more than 30MB per second - an increase to 7.5 million households from six million last year.
But higher-speed broadband is available in fewer than two in five (37%) homes in rural areas, the regulator found.
And around 8% of households, around 2.4 million, cannot receive a connection with speeds of more than 10MB per second, a figure which rises to nearly half of houses in rural areas.
This was often because caused by remote houses "lying further from the network's local street cabinet or local telephone exchange", Ofcom said.
Small businesses were struggling in particular with slower connections, as almost half are unable to achieve more than 10MB per second, and the watchdog estimated that by 2017 around 18% will still be unable to access superfast services.
According to the report, a 10MB per second connection was a "tipping point" above which customers rated their broadband as "good".
Meanwhile, "ultrafast" broadband, with speeds of more than 300MB per second, was available to around 500,000 homes in the UK.
Mobile 4G coverage has also increased across the major networks from 44% in 2014 to 73% this year, with data use on mobile growing at a faster rate than on fixed wireless networks.
Sharon White, Ofcom chief executive, said: "Mobile and broadband have become the fourth essential service, alongside gas, electricity and water. There's been a technological revolution over recent years, with 4G mobile and superfast continuing to extend across the country.
"Our challenge is to keep supporting competition and innovation, while also helping to improve coverage across the country - particularly in hard-to-reach areas, where mobile and home internet services need to improve.
"It's vital that consumers have the tools they need, such as the new Wi-Fi Checker, to get the most out of their communications."