Brighton’s official travellers site has been full in only 11 weeks out of 55, according to council figures released by Hove Conservative MP Mike Weatherley.
Mr Weatherley used a freedom of information request to obtain the figures which he said undermined the case for creating more pitches at the Horsdean site.
He said that travellers were choosing to use parks and public spaces when they could use the official site instead.
The site, close to the junction of the A27 Brighton bypass and the A23 London road, has 23 temporary pitches.
Brighton and Hove City Council plans to build 16 permanent pitches on an adjoining plot of land.
Councillor Geoffrey Theobald, leader of the opposition Conservative group on the council, is presenting a petition against the proposal to a meeting of the full council at Brighton Town Hall next Thursday (19 July).
Mr Weatherley said: “Residents are repeatedly told that the city needs more taxpayer-funded accommodation for travellers yet proof is in the pudding.
“It is patently clear that despite pitches being available over the past year travellers have still chosen to invade public spaces at no cost to them and without consequence.
“I have pledged to help residents across the city fight the Greens’ application to the South Downs National Park Authority and will shortly start an e-petition following the success of a paper petition which is to be submitted shortly at full council.”