THE firm behind controversial plans to build a £1.7bn potash mine in a national park - the UK's first in more than 40 years - has countered claims the Government should hold a public inquiry into the scheme.

Shares in Sirius Minerals fell by 12.5 per cent, after announcing the scheme in the North York Moors National Park, near Whitby, needed to overcome numerous hurdles - despite key elements of the project gaining planning permission - and adding it was examining ways of increasing capacity from 6.5m tonnes a year to 10m tonnes a year.

The firm's stock leapt by 50 per cent when it received the go-ahead from the park authority two weeks ago with planners concluding the 1.5km-deep mine's potential to create more than 1,000 jobs and generate £1.5bn a year outweighed environmental concerns.

Investors reacted again on Friday (July 10), when in a stock market update the firm said most of its applications were departures from council and park authority development plans and Secretary of State for Communities and Local Government Greg Clark still had the option to call-in the project and launch a public inquiry.

Such a move would be welcomed by numerous conservation groups, including the North Yorkshire Moors Association, which have long called for the Government to scrutinise the scheme.

A Sirius spokesman said: "The company does not believe such a course of action is necessary and awaits notification from the local authorities as to Government’s decision."

The firm added a number of steps needed to be take before the final decision notices are issued for the mine and mineral transport system to Teesside from both the park authority and Redcar and Cleveland Borough Council (RBCB), for the materials handling facility from RCBC, and for temporary construction accommodation and a park and ride facility from Scarborough Borough Council.

The company said it expected all the remaining issues to be dealt with in a "timely fashion", in order to enable all of the decision notices to be issued before the end of September.

It added a proposed development consent order for harbour facilities at Teesside would be examined by the Government's Planning Inspectorate at a preliminary hearing on July 21, and a final decision was due to be made by the Secretary of State for Transport within a year.