Zenj
Under JAR OPS 1, any Captain who flies from both seats should demonstrate the 3 minimum items of:
1. Eng Failure after V1
2. Single Eng go-around
3. Single Eng landing
If a Captain demonstrates these to a satisfactory standard then he is OK to sit in either seat. It could be that a Captain completes an OPC/LPC completely in the RHS, which if he does, he would then have to demonstrate the above 3 items from the LHS in order to operate again from both seats.
Hope this is helpful (and correct...)