In message , Paul Corfield
writes

I cannot understand why anyone would fly to somewhere like Paris.

Everyone's sums will vary according, amongst other things, to their
starting point. In my case (and travelling light as I always do):

Home to Heathrow: 30 minutes
Waiting: 90 minutes (2 hours is not necessary with advance check-in)
Journey: 75 minutes
CDG to central Paris: 45 minutes
Total: 4 hours

The figures for Eurostar from Waterloo a
30 + 40 + 160 + 10 = 4 hours

The figures for Eurostar from St Pancras will be:
55 + 40 + 135 + 10 = 4 hours

So, the sums are finely balanced. Waterloo is very convenient (virtually
a cross-platform change) while St Pancras will add a tube journey across
central London.

Eurostar is more pleasant, but catering is very basic in standard class
- the wait at Heathrow is annoying, but since it is not unexpected the
time can be used for a meal or some last-minute shopping.

Costs can be cheaper by air - BMI are currently offering £29 each way.
I've seen occasional Eurostar offers that can beat that, but they are
usually very limited.

So, I don't think decisions are necessarily clear-cut. As I've said, I
think that its a pity that Eurostar are going to abandon Waterloo - not
least because a second London terminal would give them an alternative to
closing the complete service, as happened this weekend - and also, of
course, because the inconvenience of a journey across London may tip the
balance in favour of flying from Heathrow or Gatwick for those living in
quite an arc of W/SW/S London.
--
Paul Terry