Hi Pulse;
I'm a second year Aviation Tech and Management stude, and have just started a summer palcement at a firm at a NE Airport.
When did you start applying? If you are only applying now then it is probably too late, and you should start again next year.
Who are you applying to? perhaps instead of firing off random letters/emails to "head of operations"; "Airport Manager" try to find out the name of the person in charge. at least then you know it will reach a real person. you'd be amazed at the numbre of faxes, e-mails, letters, phone calls etc that come through ops, and unless you know your letter will definately reach someones desk, chances are it will be buried. I know Servisair have names and contact details on their website (or they used to) but it takes some finding.
I would also imagine being able to get into work will be a big bonus, so i would be tempted to only apply for local companies (eg if you are south coast, perhaps Bournemouth, Southampton etc, and forget LHR unless you can make it there for some v e r y early starts).
these are pretty general guidelines / observations, i dont know what its like "darn sarf", except that it is sometimes possible, but you have to persevere ( I sent out about 30 -35 letters and only ever got one reply, which turned into this placement).
Hope this helps a little (its not much but i'd rather put down things i am certain about than conjecture)
Matty