If you have membership of the LGPS before 31 March 2014, Final Pay will be used to calculate the pension (and lump sum if applicable) for that part of your benefit.
The definition of Final Pay is very similar to Pensionable Pay, although there are two exceptions: Non-contractual overtime and additional hours are not included as part of Final Pay.
In addition, while Pensionable Pay is based on the actual pay received, for Final Pay, the calculation is based on a Whole Time Equivalent Rate, even if the member only works part time.