On this.
Firstly, 200k pax a year is the equivalent of 2 x A320 rotations a day, unless you think you can fit nearly 300 people on a daily ‘fairly small flight’. In practice I assume Manchester - Southampton was around 4-5 daily rotations of smaller aircraft. Obviously it’s not now Flybe have gone to the wall.
Secondly, look at Newcastle. Even with a half hourly train service, and journey times well under 3 hours, and a much smaller catchment population than Glasgow / Edinburgh, it still supports 5 London rotations a day and half a million passengers. Like Manchester, most of these must be transfer passengers.
So, there will be a reduction in London - Central belt flights (as there has been already), in my view around half (a couple of years after Phase 2b is complete). @Noddy disagrees, and thinks it will be a smaller reduction. But I think @Noddy and I both agree it is unlikely to be more than a halving, partly because of transfer traffic, and partly because of those passengers who have a journey that starts or concludes sufficiently close to an airport to make the flight much more attractive. I guess we’ll see. All of this, of course, assumes that the aviation industry, the rail industry, and the economy, is back to ‘normal’ by the time HS2 is open.
I said one morning and one evening flight in each direction (i.e. a total of flights a day). Chances are there were some additional flights which didn't run daily to then drop the figures more.
According to here for Flybe:
anna.aero | Temporarily Unavailable
www.anna.aero
Route Manchester – Southampton
2019 estimated passengers (MIDT) 119,474
Est. passengers daily each way (PDEW) 164
I assume that there must have been another airline providing some additional services to bring the total to the 200,000 which is seen quoted elsewhere, here: