It's probably best to ask here at the time. Unfortunately accepting a refund was perhaps a mistake since that's a remedy as an alternative to a rebooking. If BA cannot rebook you on the same day then you can recover your additional costs, but not if you accepted a refund. There is a very detailed thread here on EC261, which covers this issue. However you may be entitled to £520 for the late notice cancellation depending on the reason behind the cancellation.