C'mon, people, get real. Even the Connectivity Task Force understood the big problem;
If slots into the UK's international hub could be found for Plymouth the mothballing of the airport could be re-considered.
The word is "If".
There has been no Government policy whatsoever on increasing runway capacity at London hub airports, particularly Heathrow, and/or on building an alternative in the Thames estuary, since 2000, and there wasn't one before then either.
The 2003 study cost £100m and provided a way forward of sorts; the problem is that the conclusion of the study could have been written on a fag packet before the consultants got involved, although I'm personally very grateful to the tax-payers for the generous income that study provided for 4 years.
But the report was shelved by the Labour Government the day after it was published, for all practical purposes.
Successive announcements have been made about studies into the problem, as though the 003 study did not exist. I think there's one being planned even now, although I don't bother to keep up.
The 3rd short runway at LHR was a good solution when Charles Stuart launched it in the mid '80s; I was proud to have helped him with it. But it got nowhere in the face of stupidity, commercial and operational incompetence and competing vested interests.
That lethal combination means that no real addition to London airports' runway capacity is actually going to happen.
And that, in turn means that any hope of slots being allocated at a viable cost to routes from Plymouth to London is a pipe-dream.
If anyone is interested, the solution to the problem proposed in 2003, and shot down by BAA and NATS working together, was the 2000m parallel (to LGW) runway at Redhill, dedicated to regional services, with an 8-minute overland monorail transfer to Gatwick and a dedicated rail spur to central London from the terminal. When you see Gatwick promoting its own parallel runway, remember that in order to kill off Redhill as a competitor, BAA/NATs declared that a parallel runway could not operate safely without severe movement limitations. It was a lie, of course, but the DfT believed it.