Extra Validation

Hi,
I am trying to add extra validation in a sample db (done in A97 see attached)
I am attempting the following: Please not that the db has existing validation which I would like to keep (or change if advised) 

Conditions:
1.      Input into field “ID” must start with the letter P or p or R or r
2.      If field  “ID” starts with the letter P or p and field “Code” starts with the letter R or r, then a message stating that this combination is invalid should appear
3.      If field  “ID” starts with the letter R or r and field “Code”] starts with the letter P or p, then a message stating that this combination is invalid should appear


Grateful for assistance. Thanks
Test.mdb