Useful websites:

Royal Horticultural Society: http://www.rhs.org.uk/
Lowden Garden Centre, Shaw: http://www.lowdengardencentre.com/
National Open Gardens Scheme: http://www.ngs.org.uk/
West Kington Nurseries, Chippenham: http://www.wknurseries.co.uk/
Secret Nursery, Box: https://www.facebook.com/secretnurserybox/
Professional Gardeners' Guild: http://www.https://www.pgg.org.uk/