In recent weeks the UK government has invited residents from two communities in north-west England to a “virtual exhibition” to gauge their views on whether they would be prepared to solve one of the biggest environmental challenges facing the country: what to do with more than half a century’s worth of toxic nuclear waste.

The boroughs of Allerdale and Copeland in Cumbria are considering whether to become host to an underground storage facility for the most radioactive by-products of the country’s nuclear industry. The process, which is designed to give local residents the final say, is run by the state-owned Nuclear Decommissioning Authority.

Like other countries with nuclear industries, the UK government has been grappling with the issue of long-term storage for several decades. This marks the fourth attempt to find a site to bury radioactive waste at depths of up to 1km underground.

Any repository would have to house it for at least 100,000 years so it can decay to safe levels without the risk of human interference or natural events, such as earthquakes or a rise in sea levels, that could trigger a leak.

The UK relies on nuclear energy for 17 per cent of its electricity generation and the amount of waste will only increase as the government has ambitions for a new generation of nuclear plants to help cut carbon emissions.

The country already has more than 500,000 cubic metres of high and intermediate-level nuclear waste that has accumulated from power and weapons programmes since the second world war. Allowing for future reactors, the NDA estimates that figure would ultimately rise to 750,000 cubic metres.

The waste is kept at surface level in drums at more than 20 sites around the UK, much of it at Sellafield in Copeland, the heart of the UK’s nuclear programme.

“If you were sat right on top of one of those [high-level waste] containers you would be dead within several hours,” said Dr Clare Corkhill, an expert on underground nuclear waste storage, at Sheffield University.

Surface storage is not a long-term solution beyond much more than a 100 years. Hence the government’s insistence that it is the “right thing to do” to find a permanent solution that is safer for future generations.

Copeland was the first region in November to create a “working group” under the process overseen by the NDA aimed at engaging with the community over siting what is know as a geological disposal facility (GDF). This would store waste in metal or concrete containers sealed permanently in vaults hundreds of metres beneath solid rock.

Some nuclear experts, including those at the International Atomic Energy Agency, believe a GDF is the best method for the permanent safe disposal of spent nuclear fuel.

Copeland was followed last month by neighbouring Allerdale, home to many Sellafield employees, to consider whether to house what opponents refer to as “a nuclear dumping ground”. The NDA is hoping other communities will sign up this year.

These two councils have been here before, as two of the areas earmarked for a GDF in a process that ended in 2013 when Cumbria county council put a stop to it after tens of thousands of residents and environmentalists protested and some geologists raised questions over the suitability of the area.

The change this time is that the county council, which did not respond to a request for comment, has no such power of veto.

Supporters of the scheme argue it gives more power to communities immediately affected by a GDF as they would get the final say with a local plebiscite. But critics have derided this approach as “pork-barrel politics”, especially as communities that sign up to the process are being offered up to £2.5m a year for local initiatives.

There is as yet no cost for the scheme beyond the £12bn estimate in 2013. The NDA, which has an annual budget of £3.5bn to cover waste storage and decommissioning of old nuclear facilities, said an updated figure would depend on the final location, geology and design.

Andy Ross, director of GenR8 North, a property development company that nominated both Allerdale, where he lives, and Copeland as potential hosts of the GDF, said he was hopeful the latest process would give residents a better opportunity to understand the pros and cons of underground storage. He said the county council had also been invited to participate in the working group but had so far declined.

“A lot of people don’t understand the extent of the storage facilities now . . . It’s not as if we are bringing waste into the county and storing it. It’s actually already here,” said Ross.

But local opponents are outraged. The plans are “like a dog going back to its sick”, said Marianne Birkby, who lives 25 miles from Sellafield and runs Radiation Free Lakeland, which campaigned against the facility last time.

Reluctance to host such a facility is not unique to the UK. “The reality is nowhere in the world is there [yet] a functioning deep geological repository for spent nuclear fuel,” said Dr Paul Dorfman of University College London’s Energy Institute.

Finland looks set to be the first country to complete an underground storage site for nuclear fuel, with work having started. But it has been a long process that started in 1984. In neighbouring Sweden, plans are also advanced, although final approval is still pending — a process that has taken more than a decade.

But nuclear sceptics point to lessons from the US, where in 2014 radioactivity leaked out of an underground facility in New Mexico built to store weapons-related waste.

The latest UK search is expected to be lengthy, with detailed site investigations expected to take up to 15 years. “It seems problematic to try to do it in a rush as it were when you haven’t got the science,” said Dorfman.

But the search for a site is key to the government’s plans for nuclear power — one of its 10 flagship green policies — according to nuclear experts.

“My personal position is I don’t think we should have any new nuclear power stations until we have a [long-term] disposal strategy in place,” said Corkhill.