Update: You can ignore part of the story below the line now. Detective work by the community has revealed that the culprit is that the needed WMDRM (Windows Media Digital Rights Management) plug-in has been accidentally disabled or overwritten by one of the many platform updates issues by Nokia - and we're not sure which.
You can download the plugin here as wmdrmdlaiplayerhttppluginv1.2.1.SA_.S60.sis and it should re-install on both Belle Refresh and Belle Feature Pack 2, restoring the iPlayer DRM compatibility. Well, until the BBC do eventually stop serving up licenses....
Don't worry if you'd previously installed it - it won't do any harm installing it again, over the top.
Phew! Sorry for the premature alarm.
As of now, certainly for my test devices (E7 and 808), if you try and download a programme from BBC iPlayer, the download of the .WMV file succeeds, but then the DRM license can't be retrieved from the BBC's servers, implying that something's been finally unhooked at the Beeb's end. Ah well.
Interestingly, as you'll see from the comments below, some Symbian users are still able to connect to, and receive licenses from, the BBC's servers. It's not clear whether success or failure is dependent on the connection ISP (e.g. my Wi-fi takes the phones via Virgin Media) or on the device product codes. My guess, then, is that support is gradually being withdrawn - kind of the opposite of a 'roll out'? In time, I expect no DRM licenses to be served.
It's a sign of the times, obviously, that Symbian fell out of favour with the iPlayer team, who are evidently pushing solutions for the mass market iOS and Android platforms. Quite sad though, after almost five years of happy BBC viewing on Symbian, starting with the Nokia N96, I believe?