Daisy,
To generalize, we are talking about 'pollen beetles' and 'flower chafers', terms that cover quite a range of beetles.
The pollen beetles are mainly in the Nitidulidae and Kateretidae. They are small.
The flower chafers have the general appearance of scarabs (Scarabaeidae) but are in its subfamily Cetoniinae. These are larger.
http://en.wikipedia.org/wiki/Cetoniinae Your particular beetles are in this taxon.
It is not just the adults: the larvae can be found on flowers, too.
If you Google 'pollen beetles' and flower chafers', you'll find quite a lot of info to sift through regarding their control.
Syngenta make a product called Plenum, but it kills bees as well. I don't know if you will find anything that will kill or deter just the beetles - as Alisdair says.
Also, as the beetles are mobile and spasmodically prolific; I don't know if natural predators could be effective, at least on the scale of a garden. But specific ladybirds are used as biological control of some smaller pollen beetles (
http://www.greenplantprotection.eu/pests/field_crops/rape/meligethes_aeneus/pollen_beetle), and wolf spiders are known to predate them - so maybe there's hope.
Do tell us what you decide to do, and if you try a remedy, keep us posted on progress!