Really? OAG lists six airlines (British Midland, Ryanair, Go, British Airways, Easyjet, and ScotAirways) flying LON->GLA for a total of 51 non-stops in each direction each day. They are all roughly scheduled for about 1:15. Even with airport transfers, surely it beats even the fastest train (seems to be Virgin, just over 5 hours total via Euston; most othars are about 5:30) by several hours.
/jordan