Members of the union working for BA’s Mixed Fleet operation will strike from 22 to 25 February inclusive. This stoppage is in addition to a four-day strike from 17 to 20 February. It will take the number of days of industrial action to 19 since the start of the year.

The latest tranche of strikes ended on Saturday, after six days of walkouts in one week.

BA’s Mixed Fleet operation serves around 50 domestic, European and long-haul routes. All the staff have been recruited since the last cabin-crew dispute ended in 2010. They are employed on less favourable terms than longer-serving staff.

The cabin crew are striking over what they describe as “poverty pay”. Unite says cabin crew earn an average of £16,000, including allowances, a year. BA does not recognise this figure, saying that the lowest paid full-time member of Mixed Fleet earned more than £21,000 last year.

The impact of the strikes appears to be dwindling. During the first three days of the latest stoppage, British Airways says it cancelled a total of 24 flights; during the latter three days, only 10 were grounded. That represents less than half of one per cent of total BA flights.

Some departures have been covered by chartering in planes and crews from other airlines, including Titan and Thomson Airways.

Unite regional officer Matt Smith said: “For every hour British Airways ‘wet leases’ an aircraft from another airline to cover striking cabin crew it costs in the region of £2,000 to £3,000.

“Our estimates put the amount of money British Airways has spent on defending the dispute and poverty pay at £1m.

“This is money which the airline has taken a conscious decision to give to other airlines rather than addressing pay levels which are forcing hardworking Mixed Fleet cabin crew into financial hardship.”

The dispute affects only some flights to and from Heathrow; services from Gatwick, London City and Stansted are unaffected.

BA said: “All British Airways customers will fly to their destinations during the proposed industrial action by Mixed Fleet Unite on 17-20 February.

“To enable all customers to travel we will be merging a very small number of flights at Heathrow – about 1 per cent of total flights planned. We are contacting customers on those flights with the options available to them.

“We will publish more details over the weekend in relation to further strikes called by Mixed Fleet Unite for 22-25 February, but as in previous strikes all customers will fly to their destinations.”

The airline said its pay offer reflects pay awards given by other companies in the UK and it will ensure that rewards for Mixed Fleet “remain in line” with those for cabin crew at its competitors.

British Airways has warned strikers that they will lose their entitlement to staff travel benefits for a year.