The Essex Biodiversity Project has published a leaflet with advice on how to manage and restore existing hedgerows, and how to plant new hedgerows. The leaflet (PDF 1.6MB) can be downloaded by clicking this link.
Further advice on managing hedgerows can be seen at the Peoples Trust for Endangered Species website,
http://ptes.org/index.php?cat=61
Their related pages include a hedgerow management guide in PDF format.
Also see the Hedgelink website at http://www.hedgelink.org.uk/