British Airways boss Willie Walsh has challenged a report that the carrier is “losing more than 900 bags a day” at Heathrow Terminal 5.

In a letter to The Guardian Walsh insists: “These bags are not lost. They are bags of passengers connecting between flights which become delayed in the transfer process, often for the simple reason that the incoming flight was late.”

A union representative who worked as a baggage handler at Terminal 5 told a committee of MPs on Wednesday that on average 932 bags a day are missing their connections in transfer at the terminal – a rate of about 80 per 1,000. Unite blamed the lack of an automated system to transfer bags between terminals 4 and 5.

However, Walsh said: “The large majority of these delayed bags are flown by other carriers into other terminals for transfer to a BA flight and are not the fault of BA or T5.

“T5’s new baggage system has also allowed us to reprocess delayed bags through security more quickly and, very often, have them ready for the next flight.”

Walsh added: “Delays to transfer bags are a routine feature of every hub airport. The problem is compounded at Heathrow because its lack of spare runway capacity makes it vulnerable to flight delays.”