Train from London to Edinburgh for the end of August

www.nationalrail.co.uk

I always start with National Rail.com. It is not a third-arty reseller, like Rail Europe or Trainline. It will show you the trains and prices on the date and route you enter, then send you to the actual train company for the ticket purchase.

https://www.nationalrail.co.uk/

Any of the UK rail company websites, be it LNER (The principal operator on the route) or any other will have exactly the same schedules and fares.
The problem comes if you use any third party sites.

Also any website you see now with schedules for August is frankly either guessing or lying.
The schedules change in June. While there is unlikely to be significant change no-one (even the train operators) knows the schedules beyond June.
Also the end of August coincides with the late August public holiday. That is a favourite time to do engineering on the railways. It would be unusual for those timetables to be confirmed more than 8 weeks out.
A fact that does not deter some of the less reputable third party sites from selling you tickets anyway.

Please tell us your exact date of travel.

Please tell us where in Scotland you want to go first,

http://www.nationalrail.co.uk is the site I use to look at schedules. Then I go to the operating train company to purchase tickets. (You can buy your tickets from any train company but I prefer buying from the operators.)

August is also the time when the various festivals are on in Edinburgh and it is very very busy, so you need to check the dates of the festivals (there are several) and book your accommodation asap.

I'll reiterate isn31c's post. As isn31c said LNER is the principal train operating company on that route -- https://www.lner.co.uk/

LNER has their Perks program, where you'll get a £5 credit when you join.
https://www.lner.co.uk/tickets-savings/perks/

You can use this National Rail link to check on planned disruptions
https://www.nationalrail.co.uk/status-and-disruptions/

One last thing to note TOCs make tickets available 8-12 weeks prior to date of travel. LNER is the oddity as they post tickets for their routes earlier than other TOCs. For example tickes on LNER are available 17.5 weeks out to May 31st.

Thanks to everyone who gave me so much help this winter. I purchased my tickets easily last evening for a fast train to Edinburgh. The price difference between coach and first class was not that bad so since this is once in our lifetime we are going to ride in style.

The price difference between coach and first class was not that bad so since this is once in our lifetime we are going to ride in style.

You're going to enjoy it. I've traveled in FC a few times between London and Edinburgh. You will get a light meal and they will come around with beverage service a few times. All included.

The seats are more comfortable and it's usually quieter.

To maximise your experience try to arrive early at King's Cross and use the 1st class lounge before departure (up to 2 hours before- 1 hour Friday to Sunday)

And afterwards you are entitled to use the Edinburgh Lounge for 1 hour.