The resource is based on eight holes drilled by the National Coal Board from 1979-1983, four holes completed by NAE and more than 100km of seismic data for seam interpretation.

NAE said the major seam contained 78Mt of resources.

Consultancy Palaris estimated an average thickness of 2.2m for the seam and characteristics “favourable for underground mining”.

“The substantial resource is expected to support a significant underground mine, which will provide long-term coking coal supply to UK and western European steel mills,” NAE managing director Gary Fietz said.

“The immediate access to existing rail and port infrastructure is a huge advantage as it reduces capital investment and delivery time for the project.

“We are now focused on delivering the next phase of drilling, upgrading to an indicated resource and completing the Lochinvar scoping study.

“This is an exciting time for the project and NAE.”

The explorer aims to make Lochinvar the first major underground coking coal project in the UK for more than three decades.