To actally answer the question, it is quite an involved process.
There are I think 7 exams. It will probably take at least 3-4 months of quite intense study to complete part time, with a couple of weeks full time before the exams. Last I heard GTS in Bournemouth was a very good company to guide you through that process. Then there is a 55-hour flying course. I would actually recommend that you complete the MEP first (6 hours and a test in a multi) and fly the IR in a twin. With the resources I presume you have then at some point you might decide that a twin is more appropriate to your needs, and an MEIR is valid on a single or a multi.
IO540 is being pesimistic. With an IR, if you keep in practice, you will find that in Europe you will get in more than 95% of the time into airfields with published instrument approaches. Also a great help to get into a visual-only airfield in marginal conditions to have another plan.