The Peace Picnic comes to Hove Lawns again on Sunday the 20th July. Lasts years was a great afternoon out so hopefully this years should be as well. From what I remember there is a carnival parade through town which ends at Hove Lawns by the Peace statue. The entertainment for the afternoon consists of several stages with local bands playing, films, food plus the usual "ethnic" food and nick nack stalls. As the name suggests it has a bit of a hippy vibe but it means well.
Update: It looks like the carnival part may just have been a happy coincidence last year. That took place in Brighton last weekend.