Unions have warned that businesses and customers could face cash shortages as it urged the Bank of England to help find a solution over planned strikes at security firm G4S.

Cash delivery workers at G4S are set to strike from 3am on Monday December 5 after a majority of GMB union members voted in favour of industrial action last week.

The outsourcing firm delivers cash and coins to the likes of Barclays, HSBC, Santander, Tesco and Asda.

The security operator and outsourcing firm said it has “contingency plans” to mitigate disruption if the strike goes ahead.

On Thursday, the GMB union wrote to the Bank of England’s chief cashier warning that cash supply and security could be weakened as a result of the strike.

In the letter, the union asked the Bank whether G4S is planning to use agency staff without full CRB check and SIA Licences.

It also asked if the bank has been reassured over minimum staffing levels and assurances on holding excess cash.

The union said it believes the Bank of England pressured the company to improve its pay offer on the previous occasion G4S cash staff voted in favour of industrial action due to insurance demands regarding minimum staffing.

The company said it has no plans to use agency staff without licences in response to any action.

G4S, which was taken over by American firm Allied Universal for £3.8 billion last year, has tabled an offer of a 6.5% pay rise from January.

The company has also tabled an offer of an 8.5% rise from January, with a further increase of a minimum of 2.5% and maximum of 5%, depending on the rate of CPI inflation, to start in January 2024.

The two-year deal would see cash drivers outside of London paid £14.19 from the start of next year and a minimum of £14.55 the following year.

For cashiers, this would see pay of £10.63 from January next year and a minimum of £10.90 from 2024.

Eamon O’Hearn, GMB national officer, said: “G4S Cash staff are low paid workers doing a dangerous job, transferring the cash so many of us still rely on every day.

“All they are asking for is a wage they can live on. Where they’re not worried about their bills or providing for their families.

“These staff provide a vital service. If they walk out, there is a real risk of cash shortages over the festive period.”

A G4S spokesman said: “We’re disappointed that the GMB has refused to take our latest offer to our employees for their consideration, but we will continue to engage with both parties in the hope of reaching an amicable agreement.

“We have been in regular contact with our customers and in the event of a strike, we have contingency plans to minimise disruption to cash services across the country.”

A Bank of England spokesman said: “For security reasons we do not discuss the details of banknote distribution activities in the UK.

“The effectiveness, resilience and sustainability of that distribution, including its security, is a priority for the Bank of England and we continue to engage with relevant stakeholders, including G4S, to that end.”