A320 - Just to add to what Fresca has written; -
The LPC is valid for 1 year. The rating 'lives' for 5 years from the day of the LPC expiry, so that within that period, the pilot may 'renew' his LPC with any qualified TRE and the CAA do not specify any necessary retraining requirements; any refresher training is at the discretion of the pilot.
The TRE can sign the licence and the LST/LPC form must be submitted to the CAA (as always) but they will not levy any charge provided the TRE signed the licence.
If you did your LST on 20 Mar 03, the expiry date will be March 04 and you can therefore do another LPC (without mandatory retraining) anytime up until March 09.
After 5 years from the date LPC expiry, you must refer to the CAA who will decide what retraining is necessary.
For the bible definition, refer to Lasors. Section F4. You can e-mail FCL at the CAA but they'll just refer you to Lasors anyway.
Hope that helps.