They are blocked to all passengers because rows 10, 11 and 12 on that flight are currently the first three rows of coach and BA block the first three rows to be able to increase the size of the business class cabin. The block can be cleared anytime if the business class cabin decreases in size.

if you get one of the seats and that seat subsequently becomes part of the blocked rows when they extendi the business cabin , you will remain in that seat. However, if your seat becomes part of th e business class cabin, you will be moved. Around here we call it ‘curtain roulette’.