On behalf of 70 professionals working at the Mint, Prospect Negotiator Gareth Howells said: “This will be a retrograde step for the Mint and really is an example of Labour selling off the family silver.

“Our members view this as a direct slap in the face given that the Mint’s ability to turn itself back into a viable and profitable business in recent years is due to the co-operation and determination of the workforce.

“Their reward will be to watch millions in hard-earned profits being spent on consultants drafted in to draw up new terms and conditions, and no doubt cut jobs in a drive to cut costs and justify this privatisation.”

The union, said Howells, will seek the support of the Welsh Assembly to challenge the proposals and draw up an alternative view for the future of the Royal Mint.