On my LHR to BCN last weekend, I patiently joined the priority boarding queue at T3, which had about 5 people in it.
Nobody moved or boarded for about 2 minutes while both gate agents were busy with pax. (One seemingly had a complex visa situation, and the other had some Americans who appeared to have been offloaded from the BCN flight because BA thought they missed their flight to LHR, but they didn't - mirroring the situation in
this thread.)
Around 10 people joined the priority queue behind me.
Then, two young women walked up beside the priority boarding lane, ducked under the tensa to the side of the gate area and stood at the front of the queue.
My wife overheard them saying "if anyone challenges us just shout 'PRIORITY' really loudly".
Someone behind me shouted "Why are you special?" but the queue jumpers didn't look back.
The gate agents didn't notice since they were busy.
On board, they decided to occupy seats A and C despite having been allocated to A and B. When the occupant of C arrived, they made a big fuss about having to move their coats from the B seat into the overhead lockers.
The flight wasn't that full so they probably had no status! As it looked like TS gave many status holders travelling in pairs a row of 3.