Unfortunately a lot of the time Employers can be forced to look elsewhere for employees. It's unfortunate but these days people don't have to work in the UK. How many times do you read about someone taking a sickie off work and laughing about it? The work still has to be done and if you cannot rely on a british workforce then you employ who you can rely on.
I'm not saying it's correct or I'm supporting foreign employees over those born in this country. I'm just highlighting the trend.