Tens of thousands of patients were waiting for routine treatment at the Somerset Trust in July, figures show.
The shadow health secretary has branded the Prime Minister "inaction man" over rising waiting lists.
NHS England figures show 55,007 patients were waiting for non-urgent elective operations or treatment at Somerset NHS Foundation Trust at the end of July – up from 54,283 in June, and 46,651 in July 2022, before the trust acquired Yeovil District Foundation Trust.
Of those, 2,373 (4%) had been waiting for longer than a year.
The median waiting time from referral at an NHS Trust to treatment at the Somerset Trust was 13 weeks at the end of July – down from 14 weeks in June.
Nationally, 7.7 million people were waiting to start treatment at the end of July.
Shadow health secretary Wes Streeting said patients were waiting an "unacceptably long" time.
He added: "On the NHS, Rishi Sunak is Inaction Man, refusing to meet with doctors to end NHS strikes and adding to the Conservatives’ NHS backlog, leaving patients waiting for months on end in pain and agony."
Separate figures show 1.6 million patients in England were waiting for a key diagnostic test in July – the same as in June.
At the Somerset Trust, 12,503 patients were waiting for one of 14 standard tests, such as an MRI scan, non-obstetric ultrasound or gastroscopy at this time.
Of them, 2,866 (23%) had been waiting for at least six weeks.
Other figures show cancer patients at the Somerset Trust are not being seen quickly enough.
The NHS states 85% of cancer patients urgently referred by a GP should start treatment within 62 days.
But NHS England data shows just 71% of patients urgently referred by the NHS who received cancer treatment at the Somerset Trust in July began treatment within two months of their referral.
That was up from both 69% in June, and 63% in July 2022.
Professor Pat Price, of the CatchUpWithCancer campaign, said the cancer figures show "we are still massively short in hitting the Government’s target of no more than 85% of cancer patients waiting more than 62 days between urgent GP referral and their first treatment."
"Today’s figures reveal that nearly 40% of cancer patients are missing their life-saving cancer treatment: this is over double the Government’s own target," she added.
The Prime Minister told the BBC on Thursday ongoing strikes by NHS staff were threatening his target of cutting waiting lists in 2023, acknowledging his promise could be missed.
Professor Julian Redhead, NHS England’s national clinical director for urgent and emergency care echoed Mr Sunak's comments on the impact of industrial action.
He said: “Today’s figures show that despite ongoing pressures across the NHS, including record demand for emergency care this summer, and an increase in Covid cases during July and August, NHS staff are continuing to deliver for patients."