As it says on the NHS website... 

"If a GP needs to refer you for a physical or mental health condition, in most cases you have the legal right to choose the hospital or service you'd like to go to." https://www.nhs.uk/using-the-nhs/about-the-nhs/your-choices-in-the-nhs/

This is because, there might be a smaller waiting list at another hospital, a friend or family member has recommended the treatment at another hospital or because if you need help to recover from an operation, there is a hospital located closer to family who can help with your recovery.

Additionally, if patients opt to be treated at a hospital other than the one closest to their home, it can help bring down the waiting lists at busier hospitals as the NHS work load is spread more evenly across the country.

In my experience..... I was referred to see a specialist at a local hospital for a condition that I'd been suffering with for over 20 years. It was not immediately life threatening but was causing excrutiating pain some days and was uncomfortable the rest of the time. I called the hospital to make the appointment and they informed me that it would be a two year wait to be seen. However, they said that my GP had marked my case as urgent and so I couldn't be added to the list as a 2 year wait was too long. Instead I had to be added to an 'urgent' list which was a list where people were selected to be inserted into the main list if there was a cancellation. The urgent list was 65 weeks long, and if there weren't any cancellations then it would be 65 weeks plus the 2 years from the original list, totalling 169 weeks. Also people whose cases weren't marked as urgent would still be added to the original list. I'm sure you'll need to read that paragraph again with a coffee and a clear head  to believe it :)

After some research, we found the following website which lists all of the NHS hospitals in England https://www.myplannedcare.nhs.uk/

This website is updated weekly by each respective hospital.

For my specific condition, a number of hospitals were able to see me within 5 weeks (as oppose to the 169+ weeks that was given with my local hospital)

Imagine how quickly hospital waiting lists could be reduced, patients could be seen more quickly and the reduction in overall pressure on medical staff if NHS workload was spread across the country. The idea is actually brilliant!

After continually pushing my GP surgery and quoting the NHS website, I was eventually referred to a hospital with a smaller waiting list which I am grateful for. However they still refused to offer me the choice without reason, that they are legally obliged to do and refused to let me attend the hospital that I had chosen.