Banana Head:
Which is all fine and dandy until operational necessity requires an engine change/ Flap assembly replacement etc which prevents the A/C being ferried back out of LHR to CWL or wherever.
Might just about be workable without our lovely climate
There is no reason why Main Base should also be regarded as a Maintenance Base. If the real estate the main base engineering department stands on is excessively expensive, as in LHR, JFK, you move the engineering out to where it is more cost effective. This has taken place at LHR which needs be no more an engineering centre than just another transit network engineering department, with the heavy serious stuff done either down network or at dedicated maintenance organisations.
I am reminded of getting on a 737 at Terminal 4 early on a very cold frosty morning for the first flight of the day. The aircraft was incredibly warm (APU running all night), the Captain's seat was fully reclined, with pillow, and the headset had Capital Gold tuned in. That was 'overnight maintenance'!