Same problem for me, 25 March LGW to BGI in F. Looks as if 1 March has not sorted the issue. I called/emailed BA and these are three responses I recieved:

1. The route you are flying does not offer pre-ordering, hung up and called back to get
2. You can only order special meals like vegetarian etc, I've never heard of ordering a main course, you can only do that on board
3. Emailed You First, received a written response same as number 1 above, however they did email me the menu for the flight.

Just going to chat to the snowman in the garden as I am likely to get a more sensible response from him than anyone at BA.......