BPK-POL is the N601 Airway. You will want to listen to London Area Control Sector 28, Frequency 127.105 . This is between FL195 and FL295. London Area Control Sector 34 is on 127.880, For Flight Levels 295 and above. For FL195 and below, its London Terminal Control WELIN Sector on 130.925
Any more frequency's, just ask here or visit my website thats in my signature. Hope this helps!