Farmers left reassured about phosphate fertiliser reserves after a fact-finding trip to Morocco, the world's leading supplier.

The message to members of leading farmers' club, the Norfolk Mardlers, was that there will still be over 700 years of reserves remaining in the north African country - even as production rates are doubled during this decade.

The Norfolk party was guided round the workings of a mine by Mohamed Lidbi, northern Europe sales manager for OCP, Morocco's state owned phosphate producer, which controls 50pc of global phosphate reserves.

Eleven farmers joined the study tour which was organised by outgoing Mardlers' chairman John Fuller with the help of Bunn Fertiliser.

They learned that current production of 30m tn/year has increased by 50pc from 2011 figures on the back of a £10bn investment program, which has seen significant expansion of the mine complex at Khouribga about three hours north of Marrakesh.

And a new 180km pipeline to transport raw phosphate slurry from the mine to the coastal processing plants was commissioned last month with a view to taking annual production capacity to 40m tns/yr by 2020.

The pipeline to the coastal shipping and processing terminals, which is gravity fed, cost £300m to construct. It will see the cargo trains that shuttle the mined phosphate raw material to the port discontinued and remove the requirement to use fossil fuels to dry the freshly mined rock phosphate from 18pc to 3pc prior to transport to the coast for further processing.

Other improvements have seen a dramatic reduction in the amount of water used for phosphate extraction in the desert state to reduce the environmental impact.

OCP's recent expansion has seen new products such as a 151515 NPK compound fertiliser and animal feeds being developed. Specialist food-grade phosphoric acid products have been developed for the soft drinks markets.

Mr Fuller, who organised the trip following the club's 50th anniversary, said: 'The significant investment in new facilities was impressive with all elements of the phosphate production process being comprehensively upgraded and renewed at a time we were told that phosphate reserves in other parts of the world are becoming depleted.'

He said the visit provided reassurance to farmers concerning the security of supply.