Over 100,000 people wait weeks and months too long to perform vital scans and biopsies on the NHS.
Nearly 30,000 people are now waiting longer than the six-week target on scans in England, as figures show, and the number is increasing.
One in seven people wait more than three months, while in Scotland and Northern Ireland more than 74,500 people wait for the finish time.
Experts warn that prolonged delays in important diagnostic scans could endanger patients' health by potentially delaying life-saving treatments.
There is a shortage of radiographers due to the fact that scanning delays cause data to be inadequate to fill all of the NHS's posts.
A shortage of radiographers performing various types of critical medical scans could be held responsible for longer waiting times, experts say, because about every eleventh post in the NHS is free (photo).
Radiographers perform scans that can help diagnose serious diseases such as cancer, heart disease, lung disease, and multiple sclerosis.
MRI, CT, X-ray, and ultrasound are critical for the treatment of many deadly conditions. Delays and long waiting times can have devastating consequences.
Information obtained by the BBC as part of a Freedom of Information Request revealed that one in April for radiologists in the UK was empty by April this year.
Of 14,067 available jobs, 1,283 were unoccupied and the outdated machines were possibly responsible for the slow progress.
Richard Evans, head of the Society of Radiographers, said: "If we recognize things like cancer early, we need more diagnostics.
The NHS waiting list is the longest in 11 years
The NHS waiting list in England is the longest in eleven years, official numbers revealed in October.
Proudly 4,154,559 people – about six percent of the total British population – were waiting for hospital treatment at the end of August.
This is the highest number since August 2007, and more than 3,000 people have been waiting for routine treatments for more than a year.
NH & S departments also show that the A & E departments are getting harder for the 32nd month in a row, and waiting times for cancer treatment have been missed.
Experts warned that "alarm bells" are ringing, and the health service is breaking into another winter crisis as it bickers under "relentless pressure."
The aging population and the shortage of doctors and nurses are responsible for increasing the burden on the NHS and for longer treatment of patients.
"We have difficulty handling demand and this leads to delays for patients.
"It's not just about personnel. We have aging machines that are not as efficient as they should be. "
More than one million patients across the UK are awaiting testing, and patients in England, Scotland and Wales have the right to be seen within six weeks.
But in England now 29,000 people are waiting longer than six weeks, 9,000 more than last year.
In Scotland, the number has increased by a third to 18,500 – but the situation in Wales is reportedly improving.
It's now nine weeks in Northern Ireland, but 56,000 people are waiting longer than this – a fifth higher than last year – and 22,000 have been waiting more than six months.
"The diagnostic bottleneck already threatens the concern of many," said Emma Greenwood, director of Cancer Research UK, to the BBC.
"[It] is a challenge that needs to be tackled directly if we are serious about improving the treatment of cancer patients. "
The numbers were announced after Prime Minister Theresa May declared at the Conservative Party conference that she wanted cancer diagnoses to be faster in the future.
In a speech, she said she wanted three-quarters of cancer cases, which are diagnosed early by 2028, today about half.
In England, it is planned to attract 300 additional diagnostic radiographers and universities will receive further applications for radiography courses, Health Education England said.
A Scottish government spokesman said the BBC will spend part of its £ 4million Radiology Transformation Program on reducing waiting times.