The major digital TV switchover today in north-west England has coincided with a huge increase in dumped analogue TVs, environmental campaigners have revealed.

Figures from Cumbria county council, which administers a region of nearly half a million people, show that the number of TVs dumped at waste and recycling sites has risen by 70% in the past year. This year, the council has recycled 50,000 analogue TVs thrown away by households, of which 30,000 could have been upgraded to receive digital TV signals with a simple £20 set-top box.

Around 7 million viewers in Cumbria, Manchester, Liverpool and the rest of the Granada TV region had their analogue transmissions of BBC Two switched off in the early hours of this morning. BBC One, ITV1, Channel 4 and Five will also be permanently switched off four weeks later on 2 December from households served by the Winter Hill transmitter.

Simon Birch, who is investigating the environmental impact of the digital switchover for Ethical Consumer magazine, said: "Digital UK is currently failing to tell the public of the environmental cost of throwing away their televisions. If your existing television can be adapted to getting digital TV then don't chuck it out but buy a digital set-top box – you'll be doing the planet a favour as well as saving yourself money."

The government's Energy Saving Trust, which lists energy efficient electronic appliances, currently recommends 14 low-energy digital set-top boxes. The most efficient option for anyone with an existing TV, it said, is to buy one of those recommended boxes. However, the trust said that Ethical Consumer's concerns about the "embodied energy" of old TVs – the carbon required to manufacture them – have to be balanced against energy running costs. It added that a TV with a built-in digital tuner (IDTV) requires only one power supply and can save £7 and 20kg of carbon each year compared with an equivalent analogue TV combined with a set-top box.

A spokesperson from Digital UK, which is overseeing the digital switchover, said: "Viewers do not need to buy a new TV for switchover - virutally any set, even black and white models, can be converted using a digital set-top box. This core messgae is included in leaflets sent to homes, in television advertising and on our website. We recognise that some consumers may use switchover as an opportunity to upgrade their TV and dispose of analogue TV equipment sooner than they would otherwise have done. Where they do, Digital UK encourages consumers to buy an IDTV and recycle any old equipment."

Devon county council, which had a digital switchover this spring, saw a near doubling of dumped TVs between April and September, Ethical Consumer said. Millions of TV viewers, including those in London, are yet to undergo the digital switchover, which is due to complete across the country in 2012, freeing up valuable bandwidth for future high-definition broadcasts and other services.