This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
According to the BMReports web site the current "Metered" wind capacity - which I assume means that which is traded in the Grid's market from installations registered to the market - is 8403MW.
It has shown that number for quite some months now. It seems only to change when a new large development officially joins the grid.
Actual output is, of course, much lower than the maximum metered capacity.
As I type the report is suggest current Wind output is 315MW.
The peak output yesterday was about 3200MW.
The forecast peak for today is 3137MW (at 13:00 hrs) and the peak for tomorrow suggests 5137MW (at 23:00 hrs).
I assume the missing 4000MW will be private or corporate installations and a few large developments not yet officially metered.
Either that or the information provided is suspect but given that it is part of the Electricity trading system (afaik) that would be worrying.