I'm a bit bemused by Fo's comments.
Why is Manchester a different beast? - LPL and MAN have similar catchement areas for long haul, but within the UK for domestic routes, few travellers would make the journey to MAN from LPL - The time spend doing so is unrealistic.
Therefore a LPL-LHR link would have few implications for VLM or MAN-LHR, although it may mean less car travel between the 2.
I travel extensively, if I want to go to London I travel VLM (prior to their service starting i used Virgin Trains if I had a day or two spare).
However, if I want to travel long haul - I currently drive to LHR for a flight. Why would MAN flights be involved? I want to travel point to point wherever possible. The only tiime I use MAN is for TFS flights as they are so cheap and all other flights are Full (ie LPL and LBA).
If a LPL - LHR is initiated, I would suggest that only VIRGIN would be affected to any degree, so why the useless comparison with other areas?