Yep, I agree.. the road surface there is really lethal when cold, damp, wet, or even mildly moist let alone lorries leaving diesel too.
On a positive note, I was at crystal palace car park a few weeks ago, and had the whole car park to myself as I was on a Pool plant operators course there
It was wet, so I chucked the car around, getting the back out, catching the oversteer, feeling the understeer, and generally getting to know the handling characteristics a bit better.
Its given me a good knowledge of what happens when the Z lets go at the limit!