When should I buy my train tickets? (london to sheffield, london to paris)?

listen to your friend is the only advice i can give you.sorry

The last time we went to the UK we bought the tickets for our first days travel before we left the states. We were then told by the train personnel that they will frequently sell tickets for first class, a little more spacious, at discounted prices the day of departure, often even less than coach rates. That's how we traveled the rest of the visit. They also allow those with prepurchased tickets to upgrade to first class, at the time it was only about $20 us, I don't know what it is now. At the time it was also cheaper to travel the chunnel on a bus as they drive the bus onto the train and it's a set price for the vehicle. I don't know if this is still true, but it's worth checking! Have a blast! I envy you! Wish I were going!!!!