Well, we're back from our Eurostar trip. Thanks SO much to all who have responded above.
To summarize:
We went back to the station clutching our printout of the confirmation booking. The ticket issuer sold us 2 returns to "London International (CIV)", valid until a date in December so, presumably, open returns.
There were NO problems whatsoever on trains (SWT/Southern), the tickets were accepted at the automatic barriers without any alarm bells ringing. Eurostar was OK too
Just a few points by way of matters arising.
(a) I realise that many of you work for rail companies, but I'm an infrequent traveller and Railcard holder. Because I also have a bus pass, I use trains even more infrequently these days. I use the National Rail Enquiries and Traveline websites to plan journeys. With these websites, I'll be typing the name of a station, such as St Pancras International or London Victoria. But the ticket that I buy is NOT to these stations! (e.g. ticket machine does not know "London Victoria", it issues ticket to "London Terminals".) I do find it confusing. As we are Railcard holders, I had assumed the Railcards wouldn't be valid on Eurostar, so it didn't occur to me to ask for a through ticket from my local station!
(b) Please can someone give me the link to your glossary page? Even I can understand "TVM"
but others are puzzling ("DOO"??)
(c) About the SWT employee at my local station. Strictly he was correct to say he couldn't sell me the CIV ticket without the Eurostar ticket - I accept that. But... when we went back and he did sell me the tickets, he gave us two copies of the SWT "Any Concerns?" form (SW180) on which the following had been written:
APPRECIATION [underlined]
NOMINATE THE EMPLOYEE [his name?!?!?!]
Ticks beside "Personal Details" and "Comments"
A line through "Journey Details"
Is this standard practice? We haven't filled in the forms