Theresa May has been accused of breaking a manifesto pledge after figures showed that the number of patients in mixed-sex wards rose by 50% in a year.
Hospitals breached guidelines to put male and female patients on separate wards 1,750 times in January and February 2017, up from 1,164 occasions over the same period last year, according to NHS England figures.
The jump in "unjustified mixing" was labelled a "failure" by shadow health secretary Jonathan Ashworth, who said the Prime Minister had "given up on her manifesto promise to eliminate mixed sex wards."
The 2015 Conservative manifesto said the party will "continue to eliminate mixed-sex wards".
Mr Ashworth said: "Patients expect dignity and respect when they're being treated in hospital but this Government is letting them down.
"The Government has overseen a catastrophic collapse of patient standards and this failure on mixed-sex wards is yet another sign that England's hospitals are at breaking point.
"The Prime Minister needs to get a grip and explain what she is going to do to fix the crisis which she has created."
All NHS providers are expected to eliminate mixed-sex accommodation except where it is in the patient's best interest, according to national guidelines.
In 2015, the then prime minister David Cameron said his government had "virtually abolished" mixed-sex wards.
But since Mrs May entered Number 10 eight months ago, there have been 5,618 breaches compared with 4,259 in the whole of 2015.