Which airspace requires what RNP?
For completeness, Please refer to the following website:

https://www.uasc.com/docs/default-source/documents/whitepapers/uasc_rnp-rnav_whitepaper.pdf

Here are some extracts that allow to compare US and European requirements:


  US Airspace Requirements 
  
  The current US RNP requirements are:
  
  
  RNP-10 as described in FAA order 8400.12c
  RNP-4 as described in FAA Order 8400.33
  RNAV (RNP AR) approach authorization as defined in Advisory Circular (AC) 90-101a
  Basic RNP capability is achieved through TSO-C146 compliant equipment when installed under AC 20-138().
  
  
  RNP-10 and RNP-4 procedures are limited primarily to oceanic airspace.
  
  RNAV (RNP AR) procedures are available in the US for domestic
  operations. These procedures require approval, hence the name:
  Authorization Required (AR), formally known as Special Aircraft &amp;
  Aircrew Authorization Requirements (SAAAR) procedures.
  
  European Airspace Requirements
  
  There are two existing European RNP requirements:
  
  
  Basic-RNAV (B-RNAV), equivalent to RNP-5 (reference FAA AC 90-45A, AC 20-130, AC 20-138, and AC 25-15)
  Precision-RNAV (P-RNAV), equivalent to RNP-1.
  
  
  These requirements are defined in European Aviation Safety Agency
  (EASA) Temporary Guidance Leaflet (TGL)-10, and FAA AC 90-96A. A
  statement is required in the Aircraft Flight Manual (AFM) or AFM
  Supplement (AFMS). 
  
  For European operations, a Letter of Authorization (LOA) for all RNP
  operations, is necessary, as the requirements differ from the FAA
  requirements.