That's a damp proofing wire, and I know about those (be they snake oil or otherwise!). A "damp-proof installation cable" is presumably very different from that, but I have no idea what it is.
Me thinks you need to visit a specialist Electrical dealers such as CEF as listed in @opps response above and ask there. Yes it may cost a little more but I believe you will have a better chance of obtaining exactly what you require.
I suspect the DIY shop person you asked mistook your up to 1.5cm request for 1.5mm.
I use one of the ones you rotate around the round cable daily.
Works very well although you do need to adjust the blade depth on a scrap piece to ensure you are not cutting into the inner cores as not all insulated round cables have the same thickness insulation.
However, as I've said, I really think that 'damp-proof' must be a mis-translation of something, since it would make absolutely no sense (and would be very dangerous) for any electrical cable not to be 'damp proof', wouldn't it?
No, it's 'electrical', involving current (I presume at ELV, given that the wire is bare) going through the conductor, allegedly resulting in some sort of osmosis (or reverse osmosis) in the wall. It sounds very much like snake oil to me, but I may be wrong!
Electro Osmosis Damp Proofing systems are an expensive fraud that has been rejected by the Building Research Establishment (BRE) as useless and do not work.
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