Many takeaway shops in England with a zero rating for hygiene are among those listed on the Just Eat food ordering app, a BBC investigation has found.
Half of outlets rated as zero by the Food Standards Agency in Manchester, Bristol and London appear on the app.
A consumer rights campaigner has called for Just Eat to display the hygiene score alongside each entry.
Just Eat said it took the issue "very seriously" and will trial the ratings on its Northern Ireland listings.
The BBC investigation found:
- 20 out of the 31 takeaways rated zero in Birmingham are on Just Eat
- Nine of the 13 takeaways rated zero in Liverpool are listed there
- In Manchester, Bristol and London, half of the takeaways with a rating of zero are on the platform
Local authorities are responsible for inspecting restaurants and takeaways.
In England, Wales and Northern Ireland outlets are given a food hygiene rating ranging from zero, for "in need of urgent improvement", to five, for "food hygiene is very good".
On duty with the hygiene inspectors
"It's absolutely filthy."
That's a pretty damning assessment handed out after Ealing Council's environmental health team carried out an inspection of a pub in west London - but operations manager Helen Statham believes she has good reason.
During the visit, they found multiple food safety issues - including mice and rat droppings in a store room.
Ms Statham added: "There was no sanitiser, so they can't clean effectively. Food [was left] out at room temperature, very high-risk food like rice. And [there were] no records."
The pub has a zero hygiene rating - meaning it is in need of "urgent improvement".
But that is not just an issue for those who eat at the pub. It also offers a takeaway service - with a listing on Just Eat.
And on that app and website, it gets a four-star customer review rating - but the hygiene score is not disclosed.
What happens next differs between the nations. Restaurants in Wales and Northern Ireland must display their rating prominently.
In England, many outlets choose to do so, particularly if it shows a high score for hygiene, but it is not mandatory.
Scotland has a different system, with just three ratings - Pass, Improvement Required and Exempt Premises (which are given to premises such as newsagents or chemists that are checked but are not predominantly food businesses). Ratings are then displayed on the Food Standards Agency website.
'Serious about food safety'
Just Eat, which describes itself as "a world leader in online and mobile food ordering", said it was "actively working to raise standards".
It said the company offered free accredited food hygiene training to any restaurant that signed up to the platform.
It added: "Whenever any potential food safety issues are brought to our attention, our restaurant compliance team will review, investigate and liaise with the local authority."
The company pointed out that for each outlet, it already does include a link to the Food Standards Agency website, at the bottom of both the menu and the information page. Customers do then need to input the name and postcode of the restaurant on the FSA website to find the relevant hygiene rating.
But consumer rights campaigner Chris Emmins says he believes this is not enough and wants Just Eat to display the hygiene rating for each restaurant on their individual entry.
This is an idea that Just Eat says it is willing to try out, with a trial planned for Northern Ireland outlets, so it can "test and learn what customers want".
Mr Chris Emmins believes Just Eat also needs to lead a more active change.
"There is a duty on all businesses to safeguard their customers, and it's no good saying you are just an agent," he said.
"If that was a standard traditional business, a supermarket or a travel agent, they would be hauled over the coals considerably for a failure for that sort of lack of due diligence."
Ms Statham, from Ealing Council, added her frustration.
"Members of the public are of the view they are buying their food from that business, but I think at the same time there is a responsibility or a part to play by somewhere like Just Eat in order to help to improve those standards," she said.
Just Eat entered the FTSE 100 last year and now employs more than 2,900 staff across 12 different countries.
Food outlets pay to sign up to the platform, and, in return, Just Eat promotes the business and takes orders and payments - with the outlet charged a commission on each order.
A rating appears alongside the listings, but this is generated by collated customer scores rather than decided by Just East itself.