I'm arriving by Eurostar in St Pancras at 8 am on a Wednesday, and need to get to York.
There's a train from Kings Cross at 8.30 and 9.00. I can buy an advance ticket now for 22 pounds. How long would I need to transfer? 9.00 is probably safer.
I understand that these advance fares are only valid for a specific train; so if I miss that one, I will have to buy another ticket? I assume that buying a ticket on the day of travel would be much more expensive.

I'd get 9.00 am train (it's only 30 min later after all). Allow about 10 min for transfer, as Kings Cross adjoins St Pancras and there is no immigration as passports are checked before boarding your Eurostar. While under ticket terms you must buy a new walk-up ticket if you miss your advance fare train, they may let you on the next available service if the delay was caused by late arrival of your Eurostar, though they aren't obliged to do so (not on same ticket). Yes, walk-up fare will be nearer £100.

You can buy a combination ticket from Eurostar fr the whole journey. This would mean you are protected in case the Eurostar is late

hi, tulips,

yes, when we went to Paris on the eurostar in Jan, we were pleasantly surprised to discover that by booking our UK train tickets via the eurostar website, we were covered by the international terms of carriage which means that they are obliged to let you travel by the next available train if you miss your connection.

If you buy a ticket at the station for the 0930 train to York, the one-way fare is £87.60. This is the off-peak fare valid on the train at 0930 and on later trains (earlier trains are over £100).
If you're also going back to London by train, the off-peak return (round trip) to York is £88.60.
A through ticket from the continent to York is almost certainly a better deal.

Allow about 10 min for transfer, as Kings Cross adjoins St Pancras and there is no immigration as passports are checked before boarding your Eurostar.>

right but there are spot inspections of baggage at St Pancras and though unlikely unless you are a swarthy looking type but you could be pulled over for a lengthy baggage check in London.

Thanks for the information. I don't travel by train often, but for York it seemed like the most cost effective way (I could fly to Leeds from Brussels, but at 450 euro return). I'll look into booking through Eurostar.

And ferries from Newcastle to Ijmuiden in Holland.

Yes, but that will take a very long time, from Antwerp!

You need to enter the UK Eurostar site (when offered a choice of countries - if you don't see this, clear your cookies and go to eurostar.com again). Only on their UK site do the 130 UK towns and cities north of London appear.

This isn't because they don't want French people going to York, it's because UK train companies aren't happy accepting fares in euros, as they would have to if the through tickets were offered on the French or Belgian versions of the Euroistar site.

As to transfer time, yes, you could probably walk it in 10 minutes after the Eurostar arrives, the question is how late will the Eurostar arrive? 95% of Eurostars arrive on time or within 15 minutes (far better than airlines, which typically achieve only 63-68%) but that still means that if you allowed 25 minutes for the connection you'd have a 5% chance of missing it! So I'd take the 09:00 and have a coffee at KGX.

I booked the York ticket through National Rail in the end; could not do it through Eurostar. I will try the UK site next time, didn't know that made a difference.
Thanks for the help!