I've got an SP60 on my licence for 92 on a NSL stretch of dual carriageway. Single officer in a T5 on VASCAR. (I was actually doing 81 as verified by my GPS but that's not for here...)
Anyway, when I got my licence back I queried the code with with Devon & Cornwall police, the officer's own station, the magistrates court and the "Speeding Ticket Office", whoever the hell they are. Basically each person referred me to one of the others so I went round and round in circles. Eventually I spoke to a girl who seemed helpful:
Me: "I have just got a fixed penalty speeding ticket and my licence has been endorsed with an SP60 and I want to know why it isn't the usual SP30."
Her: "Ah, ok don't worry I'll find out why you have that code, pease hold....."
Me: "Ok, thanks..."
5 minutes later....
Her: "It means you have an undefined speeding offense"
On the plus side the insurance company treated it as an SP30 when I explained the circumstances and offered to fax them the ticket describing the offense.
One can only assume an "undefined" speeding offense means: "I've fitted you up, you know it, I know it and we know who the judge will believe"