score:9
British Airways states that your baggage will not be transferred between Heathrow and Gatwick and that you must do this yourself.
Your baggage will not be automatically forwarded so please collect all your bags before leaving Heathrow or Gatwick airport.
When you check in at Mumbai your bags will be checked to Heathrow. You will need to collect them at baggage reclaim after immigration, then check them in again with a BA agent at Gatwick for the remainder of your trip to Toronto.