Found this this morning..
Time Trial
Mercedes-Benz SLS AMG Top Gear Test Track Time Trial
Period of Availability: 2011/09/06 03:20 - 2011/09/26 18:59
Gold: Cr.500,000 Silver: Cr.350,000 Bronze: Cr.150,000
This is a time trial on the Top Gear Test Track, using the SLS AMG supercar from Mercedes-Benz. Challenge the actual laptime marked by former F1 Driver David Coulthard in the real SLS AMG! If you hit any of the cones or drive off the track, the lap time will be invalid until you start over.
SLS AMG '10
Tough challenge with just the cash reward so far as I can tell, driving the SLS AMG on Comfort: Soft tires is very tricky and a special addition with this challenge is permanently invalid laptimes if you make a booboo so you have to hit the restart switch (so if you hit a cone, go off track, etc all further laptimes are invalidated which I can only assume is an attempt to stop people cheating / glitching).
A quick run at it this morning got me a 1'20.3xx, not good enough for the Silver time (that's sub 1'20.000, gold is under 1'18.000). Pretty sure I'll be able to get it with some practice but there's very little margin for error.