forget - that just will not work at VHF!! It might do on an HF radio but he would be far better off cutting himself a simple half-wave dipole and feeding it with good co-ax. Simply sticking a long piece of wire in the back of a scanner will introduce all manner of interference.
HeathrowAirport - whether you are training or not, the law still applies so just be very careful. Should you be apprehended, Mr Plod is unlikely to accept that a 15-year old is training to be a commercial pilot!!