You can't defend a NIP, it's simply a notice.
So must identify the driver, unless you want to commit a much more serious offence and then see what the authorities offer. At that speed a course should be offered (unless you have done one in the last 3 years), otherwise you will get a conditional offer of a fixed penalty, i.e. 3 points and £100.
You of course can ignore the offers and take it to court, but unless you have a defence better than "I don't think I was going that fast", that could prove expensive.