I would think in a busy environment like the London TMA, anyone would be so foolish to endevour a track from LAM without clearance, whether it was started in the charts or not. Anyway the flight plan ends at at the ingress fix in this case LAM. Very unusual to say the least that ATC doesn't come back on the horn to inform of a hold required, with the possible exception of the A380 during early morning arrivals where exemption is given during the curfew periods.
On a different tack, why is transition levels not given during descents into LHR at least not broadcast on ATIS? Are pilots allowed to reset to QNH immediately being given a altutude below transition or to wait after passing transition? Is there any laid down procedure regarding this( in the AIP maybe)? Sorry if this is a newbe question!!!