Brighton Marina is the largest marina complex in the UK and is a convienient stopover when heading up the English Channel to Dover. The marina is part of residential appartment complex and has a small shopping centre and a large selection of restaurants (mostly chains). It has a huge supermarket in the shopping area so could be a good place to stock up.
There are two downsides to Brighton marina, the first is the entrance becomes dangerous in strong winds with any south in the direction and it has a tendency to silt up, both in the entrance and in the marina.
For more information see https://www.premiermarinas.com/UK-Marina-locations/Brighton-Marina