I would like to take a train from Paris to London and the from London to Edimburgh, but I think it is a difficult to buy the tickets online because the form at the website requests a U.K zip code. Does somebody know if it is difficult to find cheap train tickets at the same day of departure or how can get train tickets from the webpage

What websites are you using? It shouldn't be particularly difficult, and for those trips, you'll definitely save money, possibly quite a lot of it, by buying in advance.

For UK: www.nationalrail.co.uk or www.tretrainline.com - you may be able to pick up the Edinburgh ticket at Kings Cross station, the departure station for Edinburgh.

It will be very difficult to buy cheap tickets on the day of departure. I have been buying tickets over the Internet, from both qjump and thetrainline, for the past 5 years with no problems. Most recently, I bought a ticket through thetrainline for a journey later this month to Scarborough, ticket to be collected at London King's Cross. And on my last visit, I habd no problem buying a ticket from London to Brussels on the Eurostar site, for collection at London Waterloo.

using thetrainline or nationalrail should give you an option to collect your tickets at a "fasticket" machine

As for cheap tickets on the day - you can't, most of the cheap tickets have rules that state you can buy them up to 6:00pm prior to the date of travel and most of them are anyway only available on-line or via a call centre

I too have been trying to buy tickets on the sited websites for our upcoming trip. Though I indicate I'll pick up the tickets at the York station and give them my e-mail address, I cannot get past the next screen because I have a US postal code. I e-mailed GNER twice on how to get around the problem (their help screen says I can, but they must have changed the screen, it no longer matches what I see), but I never heard back.

Guys,

Thanks to everyone for the comments, but I still have the problem, I cannot use a U.K. zip code because I'm not in there I'm in the US and plan to travel to U.K. soon, so there is no option at the currently screen that allows me to buy tickets online, If somebody knows a trick to buy the tickets please let me know.

If all else fails at least go to Kings Cross at least by 6pm the night before as alanRow says and try for a discounted ticket - as soon as you get to London really - could you use your London hotel as your UK address with postal code?

thetrainline has a problem w/ US Zipcodes but you can try leaving it blank, or contact the web help email and they will help you w/ the order - I've done it several times and picked up tickets throughout the UK.