British farmers have been urged to "dramatically" increase productivity levels if they hope to survive after Brexit as they are failing to "keep pace" with European rivals and the United States.
After decades of relying on the EU subsidies, UK farmers must now boost efficiency to close a "yawning" productivity gap of £4.3bn in lost GDP, according to the Agriculture and Horticulture Development Board (AHDB).
"Currently, Britain is falling significantly behind major competitor countries in the rate of growth in productivity, with pace-setters like the USA and the Netherlands growing productivity three times faster than we are domestically," an AHDB spokesman told the Telegraph ahead of this week's Oxford Farming Conference.
He added: "A yawning productivity gap – worth over £4.3bn in lost GDP between 2000 and 2013 alone – has opened up as a result of the country failing to keep pace.
"A revolution in agricultural productivity will be needed – and fast – if we are to capitalise on Brexit, continue to feed ourselves as a nation and protect the environment."
The stark warning comes as the government draws up its post-Brexit farming strategy, which will see the UK quit the Common Agricultural Policy (CAP) and end farming subsidies from Brussels of up to £3bn per year.
Philip Hammond, the Chancellor, has said that the government will match the subsidies until 2020, at which point they are expected to be drastically reformed.
Farming chiefs say the new policy should provide the same level of funding but agree it could be allocated more efficiently through tax cuts and investment in key research areas.
The AHDB has produced a five-point plan on how to keep British farms thriving after Brexit, which includes a "nationally co-ordinated strategy for research and innovation."
It also urges farmers to take part in more training and career development courses, to help prepare them for major changes in the industry and become less dependent on subsidies.
"The evidence shows that British farmers and growers under-invest in new skills and training relative to their competitors," the AHDB's report says, pointing out that only 32pc of farm managers have taken part in such courses, compared to 68pc in Germany and 72pc in the Netherlands.
“The UK has some of the most productive, dynamic and inspirational farming and growing businesses in the world. Yet, as a whole, our industry’s rate of productivity has grown more slowly than in some of our major competitors," said Tom Hind, AHDB's chief strategy officer.
"Our sense is that the industry increasingly recognises the need to dramatically accelerate productivity growth to enable UK agriculture and horticulture to succeed in a post-Brexit world. We want this report to be the start of an urgent national debate on productivity growth."
The Common Agricultural Policy is one of the EU most expensive projects, costing nearly 40pc of the European budget - around 58bn euro (£51bn) per year.
It was set up in 1957 to sustain the EU's food supplies by boosting agricultural productivity and supports around 12m farmers across Europe.