Originally Posted by
volar
Nope, the allowance is two bags, one small laptop bag / handbag (to go under the seat in front) and a larger cabin bag (which is not guaranteed, if there is no space). BA does not restrict whether you can take a coat, hat, scarf or any other clothing in addition to your two bags. Of course you should store things sensibly which involves not taking up locker space with coats.
Where does it state that you can take a coat in addition to the two bags exactly? BA doesn’t restrict what clothing you wear (except in extremist), but if you are not wearing it, that is not included in your allowance. Now in pragmatic terms, BA will likely allow it, but could at any time stop doing so and would not be in breach on their consumer contract. Otherwise might as well carry a pile of clothes rather than pay for checked luggage ;-) yes tongue and cheek, but remember this incident? https://www.flyertalk.com/forum/british-airways-executive-club/1888679-ba-passenger-arrested-wearing-too-many-clothes.html?styleid=22
The OP asked for the rules, hence my reply, based on the actual rules and also highlighting what happens in reality.