I've just done this at Heathrow for the first time.
Booked CE on the 1730 to Manchester, noticed there was 1 CE seat remaining on the 1255 departure.
Went to the FW and asked the agent if I could change, he rang ticketing up. He kept quoting disruption only but he'll ask. Was on hold for 5 minutes when I said the BA website says you can change for free on the day. He had not heard of this, but read the wording and did it there and then!
Last edited by LancashireFlyer; Nov 27, 2023 at 4:53 am