Found a leaflet yesterday in the pub (I haven't been to a pub before so this was all new to me).
Its a Scope charity event with relatively small donation amounts required (they would like you to find donations of £50 for the 50 mile route, £100 for the £100 route).
Starts in Brighton, loops to Newhaven, Lewes and then the 50 mile route goes Westward whilst the 100 Goes to Eastbounrne and Herstmonceaux and back along the 50 mile route. Entry is £18.50 on top of that.
Visit links on www.bike-events.co.uk
The event is nothing to do with me but I might give it a go.