Managing director David Hopkins is understood to have written to clients, warning them that for the “first time in many years”, it was “necessary and unavoidable” for the operator to invoke a surcharge of between £30-£50 per head.

A Mark Warner spokesperson said: “We have no further comment to make on surcharging other than to confirm that this is reflected in the cost of holidays on sale now, which are pitched to stimulate demand within the current market.”

Under the Package Travel Regulations, tour operators are legally allowed to surcharge – increasing the price of holidays by up to 10% after booking, if their own costs increase as a result of factors such as currency fluctuations.

Following the news Esprit Ski, Ski Total and Inghams, which are all owned by Hotelplan, contacted agents to insist they guaranteed no surcharges.

A Hotelplan spokesperson added: “We stand full square behind this important message, especially after the market turbulence following the European Union referendum. We want to offer our agent partners surety, confidence and our commitment.

We know how important the ‘no surcharges’ message is to agents.”

A Crystal Ski spokesperson confirmed that it would not be levying surcharges.

Neilson also said it would not be implementing surcharges. Managing director David Taylor added: “While our winter margins are definitely under pressure following the weakening of sterling... we do not feel that levying surcharges at this stage is in the best interests of Neilson and our guests.”