Despite what S-works would have you believe, as has been said by other posters the IR(R) should certainly form a part of your training during hours building.
If you look at the relevant CAA standards documents (1 for IR and 25 for IMC) you will see that the IR(R) test standards are slightly lower, but there is no reason why you shouldn’t be able to achieve the IR standards during an IR(R) test if you’ve been trained properly. Having been issued the rating, whilst it doesn’t allow you strictly to depart or arrive in IMC as you need 1500 metres visibility, it does allow you with careful flight planning to (for example) depart from Bristol in 1500m vis and 100 ft cloud base and fly in IMC to Glasgow and land there in 1500m vis and 100ft cloud base. That is the legal part, as if you are flying SEP it would not be sensible to operate with the cloud base much below 1000ft to give yourself a bit of a chance if you have an engine failure, so in practical terms in a single the only advantage of the IR over the IR(r) in the U.K. is the ability to enter class A airspace.
Get the IR(r), making sure that the instructor who trains you has experience of operating in the real world IFR environment (and there are plenty about who do), and make sure they know why you are getting the rating. After you’ve got the rating, assuming the instructor isn’t hours building get them to do some flights with you logging the P1 time and them as “safety pilot” until you feel confident, then do a good proportion of your hours building flying cross countries like the one I suggested, disciplining yourself to fly to the IR standards and approaches to IR minimas (MDA/DA + PEC). If you do that then the IR will be far easier when you start it, and the training and some of the flying will count towards the requirements for the competency based IR training. Anyone who suggests otherwise probably has a vested interest in seeing you spend a lot of money on IR training, rather than advising you how to follow the modular CPL / IR route as cheaply and efficiently as possible.
Before anyone picks that apart, your training has to cover proper navigation, met and fuel planning and selection of alternates before you launch for Glasgow, but there is no reason that that can’t be covered in a couple of hours with an instructor who knows what they are talking about.