I note the reason why HIFU was ruled out but wonder whether this would also apply to Cryotherapy or Nanoknife. With the former, while other organs are protected, cancer cells are killed by an ice ball that forms. This is a procedure that is used more in the USA but there are a few specialists in the UK. With Nanoknife or Irreversable Electroporation (IRE) to be more precise, electrodes are placed inside the tumour and electrical impulses blow holes in the tumour crippling it. I don't know whether this is being done now in the UK and if so within the NHS. It is certainly done in Germany. If you are interested as a possible alternative to salvage surgery, you could get an opinion from the top Focal Specialist at UCLH in London who I know has knowledge of these therapies and did run a trial on Nanoknife which ended a few years ago. However, he should know where it might be available even if only privately in the UK.
So, if interested you need to act quickly or defer surgery for a time. If you contact Professor M E at UCLH don't forget to mention the 'Gold Seeds' at the outset as it's possible that these might rule out these other two forms of Focal Therapy.