It's not unusual not to hear anything back during this period. Upthread I recommended 16 days, based on some Law Commission suggestions in this area, which was based on 14 days, but 16 days gets around issues such as whether you count the first and / or last day. I don't think it much matters, you've set a deadline, and now I think you should operate on it. You are also OK to move to MCOL since BA have an ability to stop the proceedings with very little cost to themselves if they react quickly. So tomorrow I'd go ahead with MCOL. If you had CEDR in mind, then that is more complex, since they require 8 weeks to elapse from the date of the first complaint, or a deadlock letter.