Town planners this week gave the go-ahead for a property in St Aubyn's Road in Eastbourne to be converted into three two-bedroom flats.
Campaigners had argued the unique character of the road, which has a high number of guest houses, would be changed forever if developers were given the go ahead to carry on converting.
They argued the increase in the number of flats is adding to the parking congestion in the street and said their customers are finding it difficult to park.
In the last 12 months, three private residential properties have been changed into 11 flats and protesters say while a balance is good, the area will soon be saturated with flats.
Heidi Cowderoy, the chair of Eastbourne Hospitality Association, who also owns the East Beach Hotel on the corner of the seafront and St Aubyn's Road, said, "It is a nice seaside bed and breakfast road and we are very proud of that area. We don't need any more flats."
The ward councillor for the area, Steve Wallis said he was appalled conversion work on the building had been carried out before planning permission had been considered.
"I have visited the site and was astonished to discover the property has already been converted into flats and they are virtually ready to let," said Cllr Wallis.
"Developers are making a mockery of the planning process.
"People should gain planning permission and then carry out alterations."

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