I have experienced far worse on other airlines- I once had to request they clean my tray table again (in F) as it had clearly been wiped with a cloth so filthy that just touching the table made my hands smell ... that was not on BA, but the fact is that all airlines are at the mercy of contract cleaners. All you can do ius tell the crew and hope they fill out a report which may or may not get to someone at the cleaning company ...