Thanks for pointers an tips Dave. Seems that nearly 1 year later MKD told Ofcom that they were being good and Ofcom closed the case. A £5k fine would hardly be a deterrent anyway.
Mine was also to a long-standing unlisted number that has never given out.
Maybe I am being overly simplistic, but with complete UK number listings only costing £200-£300 why not class any firm's cold-call to an unlisted number ( unlisted > 18 months) as misuse, silent or otherwise. Surely then it would be clear and quick to identify repetitive misuse under subsection 6 of
http://www.opsi.gov.uk/acts/acts2003/30021--c.htm#128 (Communications Act) and the regularity of £5k fines would become a real deterrent. I feel TPS should only really be necessary to protect those with listed or recently unlisted numbers.
Ofcom takes silent call complaints automatically here
http://www.ofcom.org.uk/complain.
I am now curious as to anyone actually recently having got a non-silent call from this number or the number of rings before call was answered/abandoned, just to rule out the practice of live number pinging. But that is going way off topic here, so if anyone is bothered, PM me during the next week and I'll supplement my complaint with any useful stats.