It may be that BA was willing to transport, but the authorities (of whatever stripe they were) would not clear. It is going to be hard to make a legal argument that BA emails are legal advice to be relied on.

A better approach is to write to BA with the email and ask that in light of the incorrect information, BA make good for the loss. It is often much easier to obtain the same result without spinning legal theories which then leave BA worried about precedent-setting.