You are right about afternoon tea - absolute joke and in no way business class catering. Unfortunately, BA just don't get it and insist that customers want this stodge.

Pre-flight drink, whether water/juice or including Champagne, has never been part of the BA pre-flight CE experience. If you want this, try Comair (operating as BA) in South Africa. AFAIK this is not offered in Europe on other main airlines such as AF or LH. BA's excuses revolve around time to serve pre-flight drinks and cost due to duty if Champagne were offered, yet they have HMRC dispensation for long haul Champagne and Comair can do it in SA!

Offers of extra scones and extra drinks really depends on the crew. Neither are part of the service standard and some crews think that constant attention can be grating. If you push the call button, both (and more) should be readily available.