ACAS advice...
http://www.acas.org.uk/index.aspx?articleid=16 50
How much notice of termination must I get?
Both you and your employer are normally entitled to a minimum period of notice of termination of employment. After one month's employment, you must give your employer at least one week's notice; this minimum is unaffected by longer service. Your employer must give you:
at least one week's notice after one month's employment
two weeks after two years
three weeks after three years and so on up to 12 weeks after 12 years or more
However, you and your employer will be entitled to a longer period of notice than the statutory minimum if this is provided for in the contract of employment.
Most employees, subject to certain conditions, are entitled to certain payments during the statutory notice period. You can waive their right to notice or to payment in lieu of notice. Your employer can also waive their right to notice.