Hi Fernando
-Can a PPL pilot with a IR rating, fly IFR on a single engine within the UK?
Yes.
- What's the reason why the CAA doesn't allow comercial fights, IFR, on a single engine? safety?
The UK CAA take a very conservative and traditional approach to many things, and this is one. Dispite the overwhelming evidence of the safety of single engine turbine IFR operations, the CAA still consider it to be 'too dangerous' for Public Transport.
MJ