Camden Beach at the Roundhouse
Along the side there are beach huts for hire and tiki bars that sell summery cocktails which come at 2 for 1 on weeknights and all night Mondays. No need to go hungry either as there's an ice-cream van, a pop up fish restaurant called Fishy Business, barbecues, etc.
To keep beach-goers entertained, there are pingpong tables, badminton and boules games available. Things don't wind down when the sun goes down when DJs get things going with some beachy tunes.
With the fabulous weather we've been having this summer, who needs a Mediterranean beach anyways? London really does have it all.
You can find more info on the Roundhouse website.