Good morning! I understand that you need to work within the NHS, but I do know that others in the NHS have found more experienced surgeons.
No, from what you describe, I would not feel comfortable going forward with that surgeon. He does not have enough experience, and obviously the experience he has had has not be extremely successful.
There have been others from the UK who have had very successful surgeries, and have found a way to be referred to more experienced and capable Nissen surgeons. I suggest that you start a new post/thread that specifically indicates that you're looking for a good Nissen surgeon in your NHS system. Hopefully the members who have experience will see your post and respond.
I wish I could be of more help, but I'm in the US, and have no idea which surgeons in the NHS are the best for Nissen surgeries. I do know that people in the US who have had surgeries by incompetent surgeons have suffered serious problems and have been unhappy with the results of their surgery.
Hopefully someone will be by to give you some good advice and help you with your problem.