OK, this cannot be done. I sent an email to Eland cables to see if such a cable existed, here is the response I received (I did this via work email)
"Dear Jim,
Firstly let me say thank you for your enquiry but I am afraid to say that within current British Standards it is not possible for us, or any other manufacturer to produce a 3 core fully insulated cable that is in flat form. BS EN 3183Y/B/TQ type cables have strict controls in place and any deviation from them would make the cable non-compliant and thus we would not be allowed to sell it in the UK, across Europe and even in the United States.
Many emerging markets are adopting western imposed compliance on cable types and manufacture, some of this driven by the cable industry for cost of production reasons, but also because there is a real recognition that safety standards need to be international for many products that are produced around the world for international sales.
I am sorry but I cannot offer a solution to your problem because as far as I am aware no BASEC compliant manufacturer produces such a cable, as i have said, they would not be British Standard or European Standard compliant.
Regards
Michael Adams
Technical Specifications Engineer"
I think that closes the door on this.