If you have checked luggage CX may not allow you to short check, but other than that there should be no issues other than the potential to miss the flight.
Please also consult the hundreds of other threads on this subject.
I have checked those threads, but usually the point is to just miss the last segment on an BA flight which is already stopping at LHR.
In my case, I am trying to short check the luggage and at the same time taking a BA flight from the airport. Im just wondering if (not that I am a systems expert) I already have one booking showing on my BAEC account, wouldn't it be a possibility that I flag up as a passenger on two different bookings for the same day?
I don't want to take any chances especially with the increased security measures that might be in place considering the recent events in EU that have been happening.