Speeding M25 J14 - J13 Question

[J88]

M25 road works between J14 and J13, southbound.
This section of the road has street lighting.
There is a 40 mph speed limit, with signage, and a speeding camera.
I was caught doing 50 mph on this section. It was me, and I was speeding.

The first two 40 mph signs that start the section are NOT illuminated, other than from the street lighting. Does this mean that the speed limit is not enforceable?
Would I be able to win my case if I went to court, or do I just shut up and pay up?

[Streetcop]

As long as the signs were clear and unobstructed...the offence will be complete..

Others might argue, but I think you stand to lose more by contesting..

Street