Thanks for the reply

I have just indeed gotten off with the Doha Office, i did state the change is involuntary, having checked online there isn't availability on the QR site NRT/HND-LON for 5 days after my initial travel date. The representative confirmed this to me as well. He was very apologetic, and could only offer me travel on the day prior to my travel date. This doesn't work for me as i wont be anywhere close to Tokyo that day. He has given me the following alternatives:
1. Cancel and refund my ticket.
2. Travel 5 days after my original return.
3. Travel 1 day prior to my original return.
4. Wait and call back to see if anything opens up later.
5. Change my destination for example NRT-CDG/BRU as there is availability to these destinations.

I asked politely why is there no flights NRT-LON via Doha, when there is availability on DOH-LHR/LGW and my NRT-DOH is not cancelled and i am confirmed on that first flight He stated like previously that they cannot rebook me on just one flight, it has to be NRT/HND-DOH-LON. They would have to rebook me on all the flights on the return. I did remind him this was involuntary reroute and he confirmed that it was. I'v never experienced anything like this and do feel a little let down so close to the trip. Im guessing my best bet would be to change my destination to CDG and just book a one way ticket from there on to London. I don't think waiting for anything to open up would be smart and leaving it to chance is'nt worth it for me on this trip.