There is a 25-fold difference in the number of patients facing long waits for hospital treatment across different areas of England, an analysis shows.
The review of NHS England data, by consultancy Lane, Clark and Peacock, found Castle Point and Rochford, in Essex, had the highest proportion of people waiting over 52 weeks for care.
This was followed by Southend and Blackpool.
The analysts said the inequalities in access were "stark and widening".
The worst waits were in orthopaedics, which carries out treatment such as knee and hip replacements.
The number of people on waiting lists has been growing throughout the pandemic, with a huge rise in those waiting over a year.
By the end of March, there were nearly five million people on hospital waiting lists.
And more than 400,000 of them had been waiting over a year.
Before the pandemic, just 1,600 were in that position.
Areas with worst long waits (number per 100,000 waiting over year)
- Castle Point and Rochford - 573
- Southend - 461
- Blackpool - 450
- Waltham Forest - 422
- Norfolk and Waveney - 419
The latest review shows Castle Point and Rochford had 573 people per 100,000 waiting over a year, whereas in south-west London there were just 24.
The age of local populations will be a factor in this - those areas with some of the highest rates tended to have the oldest population, while those with the lowest rates had the youngest, who are less likely to need hospital treatment.
But Jonathan Pearson-Stuttard, who led the research, said the finding were still "extremely worrying".
"We know that for many of these conditions longer waiting times are associated with poorer long-term outcomes," he said.
"Without urgent action targeting areas with the highest unmet need, we risk a generation of patients living in poorer health."