More than 100 shared houses in Brighton are under investigation for possibly breaking licensing or planning laws.
Brighton and Hove City Council said that it was looking into “a surge of reports of unauthorised houses in multiple occupation” – also known as HMOs.
The council said: “In the 2016-17 financial year, the number of reports of unauthorised HMOs more than doubled on the previous year to 192.
“In the first three months of this year, there were 30 new cases reported.
“Planning officers are steadily working through cases. There are currently 109 live investigations.
“The council has taken on an extra member of staff to meet demand.
“Special planning permission is needed in five council wards to change family homes into shared houses for six unrelated people or fewer.
“These are typically occupied by students or other young workers.
“The wards are Hanover and Elm Grove, Hollingdean and Stanmer, Queen’s Park, Moulsecoomb and Bevendean and St Peter’s and North Laine.
“The law does not apply to such houses set up before April 2013.
“In most cases a warning letter is enough to get an unauthorised HMO closed.
“However, this year 12 enforcement notices have been issued.
“Earlier this summer, a landlord was prosecuted and had to pay £4,500 in fines and costs.
“Trevor James Ford, of Horsmonden, Kent, had let 64 Upper Lewes Road via the Brighton Accommodation Agency.
“In the key five wards, planning permission would generally be refused if a new HMO would mean an over-concentration of such premises.
“The tipping point is where a new HMO would raise the proportion of shared houses within 50 metres above 10 per cent.
“The figures come in a new report to the council’s Tourism, Development and Culture committee today (Thursday 21 September).”
Councillor Alan Robins, who chairs the committee, said: “We’re very aware that the issue of shared houses is a concern in the city.
“Students and the universities bring big cultural and economic benefits. But there’s no doubt that many HMO occupants will have quite different lifestyles and priorities to their neighbours.
“We need to be careful that doesn’t start to change the character of an area for the worse.”
The council added: “For houses with more than six unrelated people sharing, planning permission is needed all over the city.
“All HMOs also need a licence from the council’s environmental health or private sector housing departments.”