The Ryanair roster pattern, although operating under IAA rather than CAA regulations, of 5 earlies - 3 off - 5 lates - 3 off, has been working fine ever since it was introduced 5 years ago and has actually prompted many people to join the airline.
The CAA would probably consider a Ryanair roster at the acceptable limit and 5 long earlies in a row can be demanding, they are however doable and manageable on a regular basis, so no real problems there.