The CPL is valid for 5 years from the date of issue.
The SEP that will probably be on it is valid for 2 years.
The MEP (if you do it) will be valid for one year.
The requirements for keeping them both valid are on the CAA websitee, but
AFAIK, it's 12hrs within the last year, 6 PIC, 1hr with an insructor and 12 take-offs and landing.
Maybe someone knows better.
GA
Forgot to say, if you don't do the required hours in that last year, the class rating can be renewed by a flight with a class examiner.