Lives will be lost because of a shortage of specialist medicine used to detect diseases such as breast and bowel cancer.

That is the stark warning from experts who have said the lack of medical radioactive isotopes available in the UK means delays in tests to diagnose cancer.

It has also led to renewed calls for the UK to develop its own manufacturing facility, rather than rely on imports of nuclear medicines.

It follows a proposal to build a new £400m medical laboratory at the site of a former nuclear plant in north Wales.

The scheme dubbed Project Arthur would see a small-scale nuclear reactor placed at Trawsfynydd in Gwynedd, to produce the radioactive materials.

The nuclear-based medicine is used to help detect cancer tumours in patients and track the progress of the disease.

But there have been no fresh supplies available to be shipped to the UK after a reactor in the Netherlands was forced to halt production for the whole of last month.

“For every month that we don’t have diagnosis, or a person doesn’t have a diagnosis, their chances of succumbing to cancer increase by 10 per cent,” said Prof Simon Middleborough, at Bangor University’s Nuclear Futures Institute.

“It is actually resulting in people dying from this now.

“These people are not getting the diagnosis, they are not getting those cancers caught early on, cancer will spread, people will die.

“It’s going to be hundreds if not thousands due to just this month’s shortage in isotopes this time around.”

Prof Middleborough said it was why he had been backing the case for Project Arthur, which was originally unveiled by the Welsh government in January 2023.

A feasibility study was commissioned into the project, and since then a business case is being submitted to the UK government asking for the cash to approve the scheme, providing a home-grown supply of the nuclear isotopes needed for the whole of Britain.

“The business case is there, it’s not new technology, it’s old technology – we can buy it of the shelf,” said Prof Middleborough.

“It’s not just a Wales thing – it’s an across the UK thing – we’re all ready to go, it is just time to press the green button and get on with it.”

Radioisotopes can be used to diagnose cancer and treat certain types of the disease such as prostate and liver – when they are injected or swallowed and absorbed by cancers from within the body.

Using them is a very common way of treating people or diagnosing people in the NHS already.

People typically get a dose of the nuclear medicine which is put into their body and it radiates.

A gamma, for example, is a type of radiation. When it leaves the body, it can be detected to show its size and location on a scanner.

But it should not be confused with external radiotherapy where they blast tumours from outside the body with radiation.

It is estimated it would take until about 2030 to get a facility up and running, if it was approved now.

In the meantime, the UK government’s Department of Health and Social Care said it was working to address the current shortages in nuclear isotopes.

“We know this may be concerning for patients and we are working closely with the company involved to resolve the issue,” said a UK government official.

“We are also working in close partnership with NHS England and the devolved governments to distribute available stock and prioritise patients with critical needs.”

The Welsh government insisted it was still behind the proposals for Trawsfynydd, and said it was working with all partners to develop and progress plans.

“We will provide an update on progress in due course.”

However, the Plaid Cymru MP for the area, Liz Saville-Roberts said action needed to be taken sooner rather than later, to help avoid a repeat of the current isotope shortage.

“Welsh government need to be pushing the business case as hard as possible. They need to have it costed, they need to work with Bangor University who will be alongside this, and the UK government has got to recognise – yes – this will cost, but look at the cost if we don’t.”

“We are going to be talking about a cost in life.”