When I made my booking, the whole trip was in Premium Economy. This is the class where you get more space between rows and a slightly bigger seat. It is more expensive than regular economy and would not be worth it except on long haul flights of 10 to 11 hours, especially if you have two of these back-to-back.The additional expense is not prohibitive in my opinion.
What is prohibitive is Business Class (BA calls it Club World). The Business Class seat is 2 to 3 times more expensive! So when I checked in at Chennai for my long hail 10 hour 45 minute flight to London (non-stop), I was pleasantly surprised to hear an offer from the agent: "Would you like to upgrade to Club World for $430 for this sector?". This is a chunk of money but I was very tired as the scheduled departure was 5:30 AM which means check-in is at 2:30 AM which means leaving a bed at 1:00 AM to get to the airport..Essentially no sleep. So, the offer to upgrade meant I could stretch out and sleep in a bed on the flight. I accepted.
The Club World seats are regular seats but with a rest where one's feet are, large enough for a person to sit on. The seat itself slides forward (the whole seat) so one can make a bed out of the arrangement - this is by design.
Also in Club World the food is endless as is the supply of drinks. No additional charge for these. I elected a Window seat so I was completely isolated from foot traffic by the aisle seat. A divider slides up and down giving you near complete privacy. If you want to sleep on a flight, you want the window seat.
The only down side is the Window seat faces the rear of the aircraft so when you are sitting up and looking out the window, the whole view is a bit disconcerting because the plane is heading "backwards" from your point of view. So be warned of this motion sickness trigger.
I had requested a special meal in Premium Economy and the staff managed to upgrade that to Business class standards as well. Good for them! And on the ground before departure, I got to use the Business Class Lounge. While waiting for the connecting flight in London, I got to use the Lounge also. These lounges are quieter than the boarding gate area with its incessant announcements, high noise levels and so many people "in-your-face" at all times. Also, the lounge comes fully stocked with hot food and a full bar - self service! No charge.
During the flight the movie selection was average but not disappointing. The music choice was absolutely horrid. British Airways thinks people who like music from the 50's, 60's, 70's and 80's are all dead.