If I have a notice period of one month for all employees, does that still apply after eight years service?

No, is the quick answer to that. In the first month of employment, notice is immediate on both sides.

After the first month it has to increase to one week on both sides. You can keep the notice period at one week for the first year, or after the probationary period increase it to one month, but the statutory notice periods will always override what has been written in the contract, unless it is a longer notice period.

The statutory minimum for EMPLOYERS to give EMPLOYEES is one week's notice for every full year worked up to 12 weeks notice (i.e. after 12 years). If you have agreed a longer notice period due to the seniority/importance of the role concerned, that will apply, as long as it remains longer than the statutory minimum. This is particularly important to bear in mind when making staff redundant.

The statutory minimum notice for EMPLOYEES to give is only one week, no matter how long their service in your company. They may choose to give you more notice, but they are not obliged to. So unless you have a different notice period agreed in your contract of employment, then someone who has been with you for 5 years could, with accrued holiday entitlement of 5 days, leave their work place immediately they have given notice - what would you do in that situation?!

Make sure you have longer notice periods in your contracts - other ways having an employment contract can protect the business.