The firms hope that their economies of scale can drive the cost down to $2 a kg, which
recent analysis suggests could make it cost-competitive.
"Clearly recruitment is a challenge at the moment, and we're putting everything behind ensuring that we are an employer of choice; that we pay well, that we've got the right benefits, and then we've got the right bonus available to attract new staff," Mr Christou said.
"Even on London Transport, where it is supposed to be a condition of carriage, just like paying a fare, the policy is coming apart at the seams and as more people see others failing to comply, the situation will escalate quickly over the autumn," he said.
Andrew Opie, director of food and sustainability at the British Retail Consortium, also welcomed the deal but said it was "vital" that production "is restarted as soon as possible, and [CO2 is] distributed quickly to food manufacturers in need of it".