Deterring parakeets

This is one for those in SE England / London I think.
Parakeet numbers seem to have jncreased enormously in the last few years, and where even just a year or two ago they were something I only saw in parks they are now everywhere. I haven't seen or heard any other birds in the local park this year, apart from the odd pigeon, and they are now ubiquitous in gardens and streets round here.
I haven't seen much evidence of damage in my own garden yet, but that's because I'm not growing much. They are a crop pest apparently, so when I get the vegetables and fruit going next year I expect to see more of them. I am certainlg seeing far, far fewer small birds in the garden these days, and can always hear a parakeet somewhere at any given time.
My question is, has anyone found anything that might deter them?
Posts
http://www.independent.co.uk/environment/nature/parakeets-cause-problems-for-british-wildlife-2165449.html
http://www.wildlifeextra.com/go/news/parakeet-damage.html#cr
OH used to live in Effingham ( not tittering at the back ) 20 years ago they were not there, but in huge numbers there when we moved here 4 years ago.
They're a bit of a marmite bird. some love them: some hate them
They used to be a bit of a treat - a flash of exotic green, and the sound of them in the park made it feel qute tropical. But this year - perhaps due to the mild winter? - I can really see that they could be a problem. The park sounds like a tropical wildlife programme ALL the time, you can spot dozens at any given moment, and having seen them only rarely in the garden in previous years, they are now omnipresent.
Bumping this up for the links.
Parakeets numerous and noise is horrendous. Dawn chorus non existent and general impression that other birds less numerous - magpies and pigeons excepted.
Does a distress or alarm call exist that might discourage them?
In years to come if the parakeets have driven out many of our native birds there will be wringing of hands, when it is too late......
Your new 'dawn chorus' must be awful @adrian.lord39.