How much notice for employers to reduce my hours?

[Madmog]

There's a strong rumour that one of the shifts at work, which I do, is going to be totally scraped. I've been there less than a year and am entitled to 28 days notice to terminate my contract. Do they have to give me a certain amount of notice. If so, how much? Just trying to work out my money for the next few months, as I suspect this could come about soon.