In the event you're being serious, then yes, I too am completely serious. It's not as if OP is planning to have a party with an entourage of guests. It's actually a familiar request of First customers and have always respected it as being a glass of of wine or a G+T on the buddy seat before said guest tootles back off rearwards.
Ofcourse this is only if (as pointed out by others above) there is indeed a buddy seat on the particular aircraft.
Shirley I am being serious.
If this is really BA's policy, then I suppose it's reflective of the fact that we're really talking about J+.
I don't think any other reputable airline allows guests in F, drinking from the F liquor cabinet. :shrug: