Guests staying at budget hotel chains have been greeted by mouldy mattresses, stained duvets and dirty toilets, according to an investigation released today.
Ibis performed "particularly badly" according to the inspectors from Which? Holiday magazine.
Mould was growing on a mattress in its hotel on Charles Street, Manchester, while a duvet at the Portland Street Ibis, also in Manchester, had a stain which was suspected to be blood.
But it was not just the rooms which gave cause for concern.
The most unclean toilet in the report was found at the Ibis Euston, Cardington Street, London. There was urine and faeces around the edge of the toilet seat, and urine was streaked down the pedestal, the report said.
Travelodge was also criticised in the report, with three hotels in London (Grafton Place, Gray's Inn Road and King's Cross Road) and two in Manchester (Blackfriars Street and Great Ancoats Street) being visited by a researcher and microbiological technical consultant, both pretending to be ordinary guests.
The inspectors said the bathrooms were unclean, leading to concern about the bacteria found in four of the five rooms.
There were also high levels of dust under the bed in one room, while dirty hand prints and ground-in dirt were found on the walls, the report said.
Travelodge denied the bacteria, which included E. coli, was a risk for guests, and said they had never received a complaint about it.
A spokesman said a leading microbiologist had carried out an independent assessment of the Which? findings that showed the report's results would not present any health risk to customers.
He added: "We take room hygiene standards extremely seriously and have taken immediate action to remedy all of the issues raised by the Which? report.
"As well as reinforcing our strict cleaning procedures, we have introduced new processes and superior cleaning materials to further improve our normal high standards across our 360 hotels."
Three Premier Inn hotels visited in Manchester were spotless, but two of the London branches, on Duke's Road and York Way, had "room for improvement", the report said. Bacteria found in the bathrooms was of "no concern" to the inspectors, however.
Comfort Inn and Jurys Inn both performed well in the investigation, which took place within a one mile radius of London's King's Cross Station and Manchester's Piccadilly Station in September.
Lorna Cowan, editor of Which? Holiday, said: "Although this investigation was just a snapshot, it does raise concerns about the cleanliness of some budget hotel chains.
"It's clear from our research that some of the hotels are getting it right when appropriate cleaning methods are being used.
"Paying guests should be guaranteed, at the very least, a clean room.
"There doesn't seem to be one single accepted standard for hygiene in hotels across the UK, and we would like to see this change."
An Ibis spokesman said: "Ibis treats matters of cleanliness and hygiene as critically important. We were, therefore, very disappointed to see the results of the investigation which showed standards that are totally unacceptable to us.
"We have over 50 hotels and 7,000 rooms in the UK and we have clear procedures in place to ensure that housekeeping standards are to the highest levels.
"Clearly the Which? investigation indicates that those procedures are not being implemented in some cases and we have taken immediate remedial actions to ensure we deliver the standards of cleanliness that all our guests have the right to expect."
But he also added: "We have submitted the results that Which? obtained to an established independent health and safety consultant, who has confirmed that nothing in those results constitutes a danger to public health."
Paul Flaum, Premier Inn chief executive, said: "We take cleanliness and hygiene very seriously. The spotless standards achieved in our three Manchester sites are what we expect across all of our 550 hotels.
"We make an annual multimillion pound investment in auditing hygiene, cleaning, maintaining and refurbishing our hotels.
"At Premier Inn it really matters to us that people enjoy their stay and we are confident that we provide rooms that are very clean and are of excellent value for our guests."