Food delivery platforms are undermining public trust by hosting outlets with poor hygiene ratings, the Food Standards Agency has said.
The comments come after the BBC discovered hundreds of takeaways with low FSA hygiene scores available on Just Eat and Deliveroo.
The BBC research found more than 400 outlets with an FSA rating of one - in need of "major improvement".
The delivery companies say they are committed to improving standards.
Our investigation focused on the cities which offer the biggest markets for the services: Manchester, Birmingham and London.
We compared the Food Standards Agency database of restaurants and takeaways awarded a hygiene rating of one with listings that were trading on Just Eat and Deliveroo on 17 May 2019.
We found 404 takeaways rated one for hygiene across the three cities, split almost evenly between the two rivals, and with many appearing on both.
There were also 21 outlets which had been given the lowest possible hygiene rating of zero - in need of "urgent improvement", 18 on Deliveroo and three on Just Eat.
What are food hygiene ratings?
Food outlets in England, Northern Ireland and Wales are graded by the Food Hygiene Rating Scheme (FHRS).
The scheme ranks hygiene on a scale of zero to five, with five being the most hygienic.
For a premises to be given a rating of one, inspectors might find dirty surfaces, poor food handling and a lack of adequate record-keeping.
By allowing low-rated outlets on their platforms, delivery companies are "undermining trust in food", says Heather Hancock, chairwoman of the Food Standards Agency.
"They're not helping drive up standards, they're not doing the consumer a service. Convenience is fantastic but convenience at what cost?"
In her view, delivery companies should not accept restaurants with a hygiene rating below three - "generally satisfactory".
According to research from the FSA, ratings between zero and two are associated with higher levels of food-borne illness outbreaks and contamination.
Scottish establishments are graded by a different food safety standard - the Food Hygiene Information Scheme - which uses "Pass", "Improvement Required" and "Exempt Premises" categories.
A Just Eat spokesperson said: "We are at the forefront of raising food hygiene standards across the UK takeaway sector."
After a previous BBC investigation last year, Just Eat, which is the biggest of the delivery companies, said it would no longer allow zero-rated outlets on its app and pledged to remove them by 1 May 2019.
Most have now had their Just Eat accounts disabled, although they remain on the platform. However, our research conducted on 17 May found three from which food could still be ordered.
Our latest research found 259 takeaways with a one rating: 50 in Manchester, 57 in Birmingham and 152 in London.
Just Eat said: "Restaurants with a food hygiene rating of zero or one are allowed to trade on the High Street, meaning that customers can walk into any of these outlets and order food directly.
"However, we do not allow zero-rated restaurants to trade on the Just Eat platform, and are also investing more than £1m in a bespoke improvement programme for restaurants with a food hygiene rating of below three."
A Deliveroo spokesperson said: "Food safety is an absolute priority for our company and we know our customers would expect nothing less.
"Our hygiene policy requires that restaurants maintain a minimum of two stars in order to list on Deliveroo. We conduct regular checks to remove restaurants who fall below the high standards we expect, and restaurants are contractually obliged to inform us if they drop below our required ratings."
Deliveroo also says restaurants with a rating of zero are immediately removed.
Our Deliveroo investigation found 18 zero-rated outlets across the three cities.
We also found 251 outlets with a rating of one. Of these, 23 were in Manchester, 20 in Birmingham and 208 in London.
Deliveroo said that independent food safety auditors work with its one-rated listings, which are given 21 days to improve their hygiene standards before they are removed.
What happens on a hygiene inspection?
The kitchen was hot, smelly and crowded on my visit, writes Angus Crawford.
The environmental health team arrived without notice, and got straight on with the job. The manager of the restaurant had no choice, that's the law.
One officer opened a cupboard to find pots and pans encrusted with filth, mouse droppings and what looked like the remains of a cockroach.
Moving to the main zinc table where the food is prepared we ducked down underneath - I wish I hadn't.
The underside was covered in grease and dirt. Below were plastic containers with herbs and spices - the lids were filthy.
When asked about the temperature of food left out on the side, one cook produced an electronic probe, which was rusty and cannot have been used for months.
This place had a hygiene rating of one - in need of major improvement. That sticker was not on the door. Instead there was one for Deliveroo.
Low hygiene scores, high customer reviews
Many of the worst-rated restaurants for hygiene nonetheless had high customer review scores online.
The average customer score for a Deliveroo restaurant with a poor (zero or one) hygiene rating was 4.2 out of five.
For Just Eat listings with a hygiene rating of one, the average customer score was 4.7 out of six.
While it is unclear how representative the ratings were of customer base, ratings were displayed prominently on Deliveroo and Just Eat listings.