Hi David,
Yes I noticed this link between Privet and house sparrows some years ago and wrote about it. Because of resultant apathy with the media and the main bird organisations, I started my own website called:
www.sparrowsneedhedges.com
I believe cover to be essential for sparrows, it enables them to travel safely between nest site, food source, and water and allows them to socialise.
Front garden loss has decimated town sparrow populations across this country, as colonies get isolated from each other. Hedgehogs have suffered too. Privet is an evergreen and common, and so is important for all-year cover. This great loss in urban and suburban hedgerow has gone almost unnoticed. You only have to see what hedgerow loss did to the countryside wildlife after the War years ago to realise its importance.
Places that do have lots of hedges and no sparrows probably suffer from not enough nest sites, too many cats and over tidy gardens with few weeds - Districts like Hampstead Garden Suburb; where due to peer pressure from neighbours, all the gardens are too neat and there is no litter in the streets, contain expensive houses are all well maintained, so now there are hardly any sparrows left.
Conversely, all my Borough's council estates have good populations of house sparrows. Scraggly overgrown hedges, weeds and badly maintained roofs are ideal for these birds.
Please visit my site and read my articles. Take away a birds habitat and the bird will go. The myth that sparrows will happily live anywhere does not help the bird's situation. All the essential needs of the sparrow must be available.
Thanks.
Donald