Once a probationary period has been completed (usually about 2 months in most companies) a month's notice on both sides is usually the bare minimum for someone in Full Time Employment in a non trivial job in the UK. after some length of service (in the order of 5 or 10 years) that can increase to 3 or more years. Of course the employer can opt to just pay your that notice period and say farewell if you are judged a security risk, and even with this notice period in place a UK firm cannot simply "fire" you because of trivial reasons (like you manager has a hangover and doesn't like your chirpy attitude that particular day) it has to go through a process - with exceptions for gross misconduct but they are usually explicity laid out in a contract and can be validated/overturned by industrial tribunal