Sure, no issues. It’s a 2 min walk across the road. You’ve still got some margin in case the inbound train is delayed too.

I’d go through passport & security controls around 45 min before departure. Afternoons are relatively quiet too.

EDIT : the LNER train also stops for 16 min in Edinburgh so there’s a buffer there. Btw reservations are optional and free of charge in the UK (doesn’t apply to Eurostar!). Use LNER’s website.

Thanks for the information.

Thanks for the information.

Hi, if the train to KX  is on time yes it’s time to walk over to St Pancras and check in. However as a frequent user of the LNER east coast line I wouldn’t trust it as am delayed so often. 
Maybe get the earlier train south? Also we get a ‘CIV’ reservation for the LNER train to link it to your EuroStar reservation (someone else can explain that better than I can!) -you can get this in person at your local station although may need to be persistent until you find someone in the ticket office who knows what it is. 

It looks like this. Also made our seat reservations on this LNER train in the LNER app. 

I know you can buy tickets to London International CIV but, as far as I can see, the screenshot does not show a reservation or ticket but just an itinerary.