Farmers producing the nation's food will face long-term consequences from the summer's heatwave, according to a Gloucestershire-based expert.

The warning comes just days after the NFU (National Union of Famers) hosted an emergency drought summit with representatives from Defra, the Environment Agency (EA), Natural England, the RPA and other farming organisations.

Dr Nicola Cannon, a principal lecturer in Agronomy at the Royal Agricultural University (RAU), said the drought would affect farmers crops and livestock nutrition.

"The extreme heat and very dry conditions are affecting agriculture in many ways and the impact of this extreme weather is going to be felt for months to come.

"The most important months for crop growth in the United Kingdom are May to August as temperatures, day length and weather are normally optimal for plant growth.

"Arable crops are generally being reported as about 20 per cent down on normal yields."

Speaking at the NFU summit Minette Batters, the union's president, told those present, including the Secretary of State for Food and the Environment Michael Gove: "The impacts of the dry and hot weather have been hugely challenging for many farms across the country, with many not seeing such weather in their lifetimes.

"As we move towards a new domestic agricultural policy it's vital that market failure and volatility are treated seriously alongside productivity and delivering for the environment."

Dr Cannon added: "Many farmers with livestock on their farm are really struggling as there is insufficient grass and forage currently growing to meet their nutritional requirements.

"This has serious implications as not only is it an extra job to feed livestock now but also they are currently eating the food that was being preserved for winter feeding.

"This is creating uncertainty about what livestock will eat later in the year. Not only this, but grass and other forage crops have had very limited regrowth following first silage cut meaning there is little available to take subsequent cuts to store for winter feed.

"Whilst most of the arable crops for 2018 have now completed the majority of their growing and have either already been harvested or are ripening up for harvest, fruit and vegetable growers are really suffering.

"Water for irrigation has almost run out and temperatures have been so high in the day that it can be difficult to apply water without damaging the plants.

"Harvest is earlier than usual as crops died off prematurely due to water stress. Oilseeds and grains have been harvested at very low moisture contents, and so have not required drying, but this means that farmers have lower yields to sell as there is less water retained in the crop.

"The challenge for UK farmers is knowing what weather is likely to occur in a season and it changes year by year.

"It's now time to look ahead to the 2019 harvest and the first fields of oilseed rape would normally be planted from 15 August. However, where soils are so dry it can require greater quantities of fuel and power to cultivate the soil and there is such limited moisture in the soil that any seed planted is unlikely to germinate quickly.

"That means it is more prone to pest problems, often has reduced vigour and uneven establishment - if it can establish at all."