A sudden power surge in reactor number four at Chernobyl nuclear plant just after 1am on April 26, 1986, caused a fatal increase in heat that led to the worst nuclear disaster in history. 

The subsequent explosion released large quantities of radioactive substances into the air for about 10 days. 

Within a few weeks of the accident 30 workers died and over 100 others suffered radiation injuries, according to the United Nation's Scientific Committee on the Effects of Atomic Radiation.

Estimates of deaths, both direct and indirect, vary wildly from 4,000 to half a million as the leak was blamed for thousands of cancer cases that developed across swathes of Ukraine, Russia and Belarus. 

Hundreds of thousands of people had to leave their homes, not knowing if they would ever be able to return. 

About 115,000 people from the areas surrounding the reactor were relocated in the year of the disaster alone. About 220,000 more from Belarus, the Russian Federation and Ukraine were subsequently moved. 

The effects of the disaster were far reaching and long lasting. The plume of released radioactive particles drifted towards north west Europe where it fell on the UK's uplands during a period of heavy rainfall six days later. 

Although the accident occurred 3,000 miles away, it had wide reaching implications for the Lake District’s sheep farmers until as late as 2012. 

There were 9,800 UK holdings and more than four million sheep placed under restriction following the accident. Sheep on eight farms in Cumbria and 327 farms in North Wales were still subject to testing until June 2012.

One of the last farms where restrictions were lifted was at High Nook Farm at Loweswater. Livestock monitoring was imposed on David Allen’s (CORR) Lake District hill farm, then tenanted by his father, Ted Allen.

David said he remembered hearing about the disaster when he and his dad were walking the ewes and lambs out on a wet April day. But he never thought the explosion would affect him thousands of miles away on a farm in Cumbria.

He said: "To be quite honest, even if you thought it was going to [affect you], in lambing time you don't worry what might happen in the future, it's what needs doing now."

Mr Allen said the farmers most affected were those who wanted to sell their sheep in the summer of 1986 because it took until the autumn for DEFRA, or the Ministry of Agriculture, Fisheries and Food as it was then, to establish a system for live monitoring of sheep. 

Farmers could not sell sheep or lambs in the summer but by the autumn sales, the system was in place. Although no sheep failed a radioactivity test on the farm after 1988, about one third of the farm's land remained under restrictions until 2012, meaning any sheep that had grazed their had to be monitored before they could be sold.  

Kevin Holliday and his wife Yvonne were also among those affected, though their flock only had to be monitored for two years. The couple had taken on the tenancy of their fell farm at Strudda Bank on Cold Fell, near Calderbridge, just a month earlier and were enduring one of the worst springs in living memory. 

"It rained every day of lambing time that year," says Kevin. "Then the sirens went off at Sellafield and we were advised to stay indoors. But what could we do? We had sheep lambing and we couldn't leave them. We had to carry on or we would have lost them." 

Restrictions were immediately placed on the movement and sale of sheep in the most affected areas. A radioactive limit of 1,000 Becquerels per kilogram was set per animal and a 'mark and release' scheme introduced. 

Sheep were monitored by ministry officials with a Geiger counter and any 'hot' sheep marked with blue paint. Farmers were paid £1.30 for every animal tested. 

"Looking back, it's hard to believe what a horrendous time we had that spring and in the months afterwards," says Kevin. 

The disaster was brought even closer to home when, 10 years later, Kevin and his family welcomed two little girls from Belarus into their home for a six-week visit. 

"Harecroft Hall School was bringing over children affected and we volunteered to be hosts," says Kevin. "They came through the door looking like little white ghosts. We looked after them, fed them up and got them outside on the farm haymaking and among the sheep." 

Seventy per cent of the total radioactive fallout from Chernobyl fell on nearly one-quarter of Belarus. According to the UN, the fallout affected more than 2.2 million people including 500,000 children. 

In the years following the disaster, Cumbrians have been opening their homes to children who continue to live with the legacy of Chernobyl. 

Nick Wilson, from Dearham, is chairman of the North West Cumbria branch of the Friends of Chernobyl's Children. Every summer, the Cockermouth-based group flies over disadvantaged children to spend a month in Cumbria. 

The children, who are aged between seven and 11, can return for up to three years before another child takes their place. Many suffer health problems as a result of the fall-out. 

Nick and his wife Kate have been involved with the charity since 1999; just two years after it was formed. The couple, who have two children Peter, 20, and Nichola, 26, hosted children for several years before taking organising and fundraising roles with the charity. 

"It gives you a real understanding of what their lives are like," says Nick. "Many families rely on home-grown food which is grown in contaminated soil. The children arrive here with practically nothing because they don't own anything. Just a month of fresh air and good food can make a real difference in their lives. 

"We've stayed in touch with some of the children and one of them, Karina, is now studying law at university."

The charity must raise about £800 to £900 a child to pay for air fares, buses, clothing and activities. Local businesses, including opticians and dentists, generously donate their services for free, and funds are raised through charity events throughout the year. 

This year, 11 children are due to arrive on Saturday, June 18. Their busy programme of activities include walks, days out at the beach, barbecues, a visit to the Brathay Trust in Ambleside, and a trip on the Ravenglass and Eskdale Railway. 

"We couldn’t do it without the support of the community and local businesses," Nick adds.

The Friends of Chernobyl’s Children is looking for volunteers and support for fundraising activities. See www.nwcumbriafocc.org.uk or FOCCNWCumbria on Facebook or call 07702490619.