According to this page, physicist Brian Cox got a D in maths for his A levels. The paragraph is repeated below:
Lastly, scientist Professor Brian Cox (whose Wonders Of The Solar System can currently be seen on Sundays on BBC Two) reveals he failed Maths A level: “I got a D… I was really not very good… I found out you need to practise.” He also believes children should enjoy science: “We need to get over [that] it’s not that difficult.”
I tried to find the video on youtube and watched an enjoyable 19 minute clip. But the quote is not there as already forewarned by page from bbc which inserted the footnote: These quotes are taken verbatim from a studio recording and may not necessarily reflect the content of the final transmitted version of the programme.