"Employment

Daniel has been working for Three Sixty Ltd for 18 months but his employment contract does not specify a notice period in the event of termination.
What is the minimum period of notice to which he is entitled under the Employment rights Act 1996?
a) At least 5 days
b) At least 1 week
c) At least 28 days
d) At least 1 month
Is the minimum period of notice specified under employment law, what is the minimum period in this question and also does employment period changes with the length of time a person is in employment. In this question the period specified is 18 months, had it been something else what would be the minimum period of notice. I mean what is the spacterum for different lengths of employment.