That's a question that is dependent on geographical distance, driving distance, and driving time. TO find out the answer for myself, I came up with the following using Google.
Nearest beaches to King's Street, Twickenham
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In summary, from the above names, Canvey Island is the closest, but Brighton is the quickest drive.
Brighton to the South or Southend to the East.
Southport
Great Yarmouth.The Britannia Monument is a commemorative column built as a memorial to Admiral Nelson, situated on the Denes, Great Yarmouth, Norfolk.
Mombassa
Promonade
Malaga, Spain
Alicante
Blackpool has 10 million visitors a year making it far and away the most popular seaside resort in the UK.
Port Erin
Perranporth is a small seaside resort, not a city
Great Yarmouth
Yes. London is not a seaside town.
Ventnor is a seaside resort on the Isle of Wight.