This is an outgrowth of funding services essential to the operation of the economy through other than general tax revenue. No matter how one slices the costs of operating the airport, if it is not funded by general tax revenues, it is then funded through user fees. Whether those are imposed on the end user, e.g., passenger or service provider, e.g. air carrier (BA in this case) is a matter of how the total price is broken down, not the total price.
Putting aside the pandemic and its impact on passenger traffic, recent history suggests that government-imposed taxes do not appreciably impact total revenue because higher PRASM fare buckets are less affected and those are what make a profit.