4greens
'cockpit napping' is known to the CAA as 'controlled rest.' The CAA as the current regulator allows any AOC holder to provide for controlled rest. It is written into their General Manual Part A section 7 which is the legally binding section of flight time limitations as applicable to that company. This section can, if it can be shown to be safe, be significantly different from the example shown in CAP 371.
FYI the CAA has no blanket rules for Flight Time Limitations. CAP 371 states that a scheme must be set up as part of the company manual and that it must be approved by the CAA, it then goes on to give examples of what would be acceptable.