Class 1 NICs : Earnings of employees and office holders : Payments to miners and former miners in place of concessionary fuel
You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals.
Regulation 25 and paragraph 14 of Part X of Schedule 3 to the Social Security(Contributions) Regulations 2001
Payments made to miners and former miners in lieu of coal or smokeless fuel, which are disregarded for tax purposes, (see EIM 66690 (SE66690)) are also disregarded for NICs purposes.
This exemption does not apply to Northern Ireland