The consumer magazine ask its members to rate coastal destinations on their beaches, attractions, value for money, peace and quiet, and scenery.
Each category is scored with a rating out of five stars.
Southsea was rated the joint 12th worst seaside town by Which? members – along with Hastings in East Sussex and Dawlish in Devon.
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It had a 65 per cent customer score and the beach was rated just two stars out of five, which is one less than Skegness’s beach was given.
Southsea’s attractions were rated four out of five stars.
However it was also rated two stars for its scenery, value for money and peace and quiet.
Jill Norman, who runs Clarence Pier, has jumped to Southsea’s defence, calling it the ‘jewel in Portsmouth’s crown’.
She said: ‘I simply don’t understand this survey result – I’m surprised by it and also disappointed.
‘I have lived in Portsmouth all my life and Southsea is the most beautiful place I know. Southsea Common gives us plenty of green space to enjoy, there’s an abundance of attractions and other towns I’ve been to don’t hold a candle to our home.
‘Our water quality has significantly improved over the past few years, so I’m surprised that wasn’t considered.’
More than 4,061 people responded and Bamburgh in Northumberland was named the best seaside town in the country in the list published on May 11.
Dartmouth in Devon and Tynemouth in Tyne and Wear were joint second.
They were followed by St Andrews in Fife in third place, with Aberaeron in Wales was in fourth.
North Berwick and Rye, in East Sussex, were in joint fifth place.
At the other end of the list Skegness in Lincolnshire was named the worst seaside town in the UK with one star ratings for attractions, scenery, peace and quiet and value for money. The beach however was rated three out of five.
Southsea was ranked lower than Hampshire neighbours Lymington – where Portsmouth City Council leader, Cllr Gerald Vernon-Jackson, is originally from.
He said: ‘I personally think those are the wrong way around; Southsea is absolutely lovely.
‘We have a great mix of wonderful history with the war memorial, a brilliant community and fabulous seafront.
‘Southsea is much better than Lymington in so many ways, so I think whoever filled in the survey got it very wrong.’
Portsmouth South MP Stephen Morgan agrees that the survey grossly misrepresents how good Southsea actually is.
He said: ‘This is nonsense, way off the mark and residents know that.
‘Anyone who has been to Southsea under normal circumstances knows the fantastic views, bars and restaurants there are for all to enjoy at one of the best destinations on the south coast.
‘It’s why I have launched my Pride in Portsmouth initiative. When they feel safe to do so, visitors should come and see for themselves how wrong this survey is.
‘Of course our city needs to be included in the levelling-up agenda for regeneration, but this is quite clearly wrong.’
The average price of hotels in Southsea is £77, according to Which?
Littlehampton was also featured – and is the ninth worst seaside town in the UK, according to the list.
Ian Clarke, owner of Southsea Beach Cafe, added that the low ranking in the survey for Southsea’s scenery is ill-judged.
He said: ‘You look out to the Solent and there is so much activity – it’s really second to none.
‘I was really surprised to see Southsea so far down in the survey when it’s such a fantastic place.
‘Credit to the council as well because there’s a lot that goes on at the seafront, from Victorious Festival to Beach Dubbin and the America’s Cup. The food scene is doing well too, with so many independents making a name for themselves.’