These are not BA stats, they are from HAL. There is a defined concept of OTD and OTA, and various triggers can put that to a "not on time" status, including the factors you mentioned. The data is pretty granular and goes to things like when the captain requests pushback, when that's OK'd by ATC, off chocs, taxi time, take off time. For arriving it also includes things like "first bag off" and "last bag off".

Today is still holding up somewhat, OTD is 73%, n=159, OTA is 69% n=156. Generally I see these figures getting worse during the day, as delays build up, the UK isn't the only place with assorted ATC issues. I certainly agree that BA's overall punctuality has taken a big hit since 2019. OK, it was super fantastic during the worst days of the pandemic, easy when the skies are empty, but I know BA's managers are frustrated with it more than (random example) no cognac in First. They've tried various initiatives in recent months and very little seems to work.