If you look on FlightRadar24 this will (probably) give you the tail number of the aircraft that's allocated to your flight. If you then search for that tail number it will show you what the aircraft is currently up to, and its next scheduled movements. Not infallible, as these are always subject to change, but it should give you a good indication.

Currently FR24 shows BA2855 as departing on time and operated by G-GATS. This is currently shown as en route from PMI to LGW, expected to land 20 mins early, so any delay notification doesn't look like it's due to a late inbound aircraft.
[Edited to add: beaten to it while I was typing!]