“It’s like a tinderbox out here,” says Lesley Chandler, looking down at parched fields where bleached-out grass struggles through baked, stone-hard earth. “Just a spark could set it all alight.”

Chandler farms 200 acres of arable land in Oxfordshire, where there has been virtually no rain for weeks. Pastures that would normally boast grass nearly a foot tall have instead a thin cover of dried-out vegetation.

The picture is the same across much of Britain, as the long, hot spell of the last two months has made the first half of this summer, from the beginning of June to mid-July, the driest in the UK since records began.

But while livestock can be fed on winter feed, known as silage, and have their troughs filled with drinking water, and some crops can be harvested early to mitigate losses, wildfire is now an over-riding concern for many farmers. On land this dry, with weather this hot, fires can catch quickly and spread fast, long before farmers can get to the bowsers – mobile water containers with a hose attachment – they are keeping filled at the ready nearby.

The National Farmers’ Union (NFU) has urged the public and farmers to be vigilant, and report immediately any fires they see, even if small. Recent disastrous fires at Saddleworth Moor, Winter Hill and Marlow have illustrated the dangers.

While open moorland is at particular risk, with few breaks to provide obstacles to the spread of the fire, farmland – both pasture and arable land sown with crops such as wheat and barley – now has few protections left after weeks of drought and high temperatures. Crops will be particularly vulnerable as they are ripening at present, drying out under the sun.

Marlborough, Wiltshire: crops are particularly vulnerable to fire as they ripen. Photograph: Matt Cardy/Getty Images

Even harvesting crops can be a danger in itself, adds Chandler. “The combine [harvester] blades can strike a stone on the field and create a spark, which could be enough to start a fire in these conditions,” she warned.

The NFU has urged farmers to take extra precautions, such as checking they are carrying working fire extinguishers on all farm vehicles and all vehicles involved in the harvest. Firebreaks should be put around fields as soon as they are harvested, to stop fires spreading among the dry stubble.

Guy Smith, deputy president of the NFU, said: “With much of the country affected by this remarkable run of weather, we’re seeing widespread tinderbox conditions. That’s leading to a significant increase in the numbers of wildfires, and that risk is only going to increase as crops ripen.”

Having a store of water close by the fields, for instance in bowsers, is essential for quick action if any fires do break out. It is particularly important in the many areas where streams, ponds and ditches and other water sources have dried up or dwindled.

It is not only farmers who need to take care. Most wildfires are caused by people, whether through carelessness or deliberately. Local authorities have warned people to avoid lighting fires in the countryside, to ensure any barbecues are enjoyed in safe conditions away from vulnerable fields, and are put out thoroughly afterwards.

People carelessly tossing cigarette butts from cars is a particular bugbear for the Chandlers, who have several fields which lie alongside roads frequented by trippers and tourists. To reduce this risk, they have cut down the verges next to the roads, which would normally be allowed to grow high to provide a habitat for wildlife and wildflowers attractive to bees and other pollinators.

Some farmers are cutting down verges next to the roads on their land that would normally provide a habitat for nature. Photograph: Joss Barratt/Plantlife/PA

In place of these habitats, the Chandlers are able to leave other areas of their farm as natural habitats, but many farmers may not have this option.

Visitors to the countryside are also being asked to report to the police or fire authorities any activities they see, such as lighting fires or careless barbecues, that could be a hazard.

The Ramblers, the walking charity, has also urged its members to help. Tompion Platt, director of advocacy and engagement, said: “It’s more important than ever to be extra vigilant for fire risks. Walkers can help by keeping an eye out for things like broken glass that can start fires, and reporting any fires that appear to be unattended as quickly as possible.”

The NFU and local authorities have also placed water bowsers in some areas across the country where there are particular attractions for visitors. But farming leaders said more was needed, including more fire wardens to monitor the conditions, and a review of the “fire severity index”, which allows areas of the countryside to be closed off to visitors if the risk reaches high levels.