Cleared to FL but told to descend

[GodAtum 69]

I was cleared to FL130, took off, and when I was at FL110 ATC told me to descend to 6000. Out of EGLL, 27L, on SID DET2G. using latest version.

[Dave-Pilot2ATC 870]

The clearance is to climb to FL130 via the DET2G departure.  This means you must abide by any altitude restrictions in the SID.  There is an At or Below restriction of 6000 ft all the way to DET that ATC was trying to enforce. 

Once past the restriction, then you are cleared to continue the climb.