It's only failing to identify the traffic for some VoIP clients.
That's why I said it's strange. The OP tried X-Lite and the traffic showed up as titanium for him.
The only traffic that should be classified as bronze, according to Plusnet's latest
traffic prioritisation scheme, is p2p/usenet (or are there still different priority schemes applied to legacy products?).
I'm just wondering how VoIP traffic is identified and classified... It can't be based on port number (lots of different ports used for RTP). It can't be based on DPI identifying an RTP stream, since other streaming traffic types are supposed to be classified as Gold. So I'm wondering if it's based on looking for the SIP transactions that set up the RTP stream...? Are you, by any chance, using a non-standard SIP port (ie not 5060)?
Perhaps one of the Plusnet reps could explain how it's supposed to work?