Here's a free travel tip: next time you want to plan a train journey, use the Deutsche Bahn website. Seriously. Even if you're travelling entirely in the UK. It is more accurate than the National Rail enquiries website, as I discovered when planning a journey from London to Northallerton today. the British website suggested we take a train leaving 5 minutes before our Eurostar arrived, or offered the attractive option of waiting in the station until early the next morning. I had a sneaking suspicion that even in the UK trains leave the capital more than twice a day. A quick look on the DB site showed one running about an hour after we arrived. I called National Rail Enquiries with some trepidation (In Germany I call helplines as a last resort: they take ages to pick up the phone, operators are frequently unpleasant and unhelpful, and they charge premium rates) But the person on the other end was very friendly and confirmed this train was running. Perhaps they use DB too. I'm told British station staff often do.
This being the brave new world of the privatised rail network, National Rail Enquiries couldn't reserve a seat so I was connected to the train operating company help desk and I had a nice chat with 'Norman', who was very apologetic but said to reserve seats with a Britrail pass like the one we are travelling with, you have to go to London Kings Cross ticket office in person. Now call me awkward if you will, but this seems an odd requirement for a ticket which is not available to residents of the UK.
Norman was as helpful as he could be, and suggested we go to coaches 'G' and 'H', because of there is space it will usually be there, and that we talk to the conductor to find where there are some free seats.
So it seems that UK officialdom (as represented by the NR website and rules) is its usual haphazard self, but the people on the end of the phone are friendly and efficient. It will be interesting to see how this works over the three weeks of fairly extensive train travel while we are in the UK.