Had you been able to put your duty free in your hold baggage I think this would have been OK. It gets screened as well.

It is very easy to reseal anything like perfume to make it look unopened. There is a limit on the volume of liquid that can be carried for well documented reasons.

In the UK, duty free is security checked and sealed to ensure that it is what it says it is. You can't get through from Landside to Airside with Duty free from anywhere else. Tansfer pax are not all rescreened if deemed to be clean. I would suggest next time you check in the duty free bags in a holdall or something. You can check with the airline if this is OK. If Security don't like it the net result will be the same but you might have a claim for lost baggage?