ROB x38
The IMC rating is not an IR, but allows most of the IR privileges outside controlled airspace, and in Classes D and E.
The IMC rating effectivelly removes the 3 Km visibility limitation imposed on PPL holders, but imposes the 1800 metres limit when flying below cloud, for take off and landing.
The UK SVFR minima is 10 Km for PPL holders, this reduces to 3 Km for IMC rating holders.
Holders of JAA PPLs issued by States other than the UK have a license visibility minima of 1500 metres!