Flight cancellation and rebooking - my rights?

We wanted to go to Grenada in November/December but because it was cheaper to book a package rather than direct with the hotel and VS, we decided to try VH. Unfortunately they had no UC seats available so we chose to book the lot with BA, paying a hefty deposit.
Quite by chance, I checked my BA booking and both flights have been cancelled and we have been rebooked on flights that are over 2 hours earlier, which is tricky for us on that day, but also different flight numbers. The blurb says we can accept the alternative booking, rebook another flight at no charge, or cancel. VH also have now got UC seats available for our chosen dates.
Does anyone know whether we really can cancel and get our deposit back? Are there rules? Obviously we won't change to VS/ VH unless we can be certain of getting this deposit back, but VS/VH would suit us much better and as a bonus we'd move up a FF level and get the miles we collect too.
Quite by chance, I checked my BA booking and both flights have been cancelled and we have been rebooked on flights that are over 2 hours earlier, which is tricky for us on that day, but also different flight numbers. The blurb says we can accept the alternative booking, rebook another flight at no charge, or cancel. VH also have now got UC seats available for our chosen dates.
Does anyone know whether we really can cancel and get our deposit back? Are there rules? Obviously we won't change to VS/ VH unless we can be certain of getting this deposit back, but VS/VH would suit us much better and as a bonus we'd move up a FF level and get the miles we collect too.