An Infringement Notice is in effect an allegation.
You can go to court to contest that allegation
(the bit on the back where you "court elect" the offence).
And yes, they can "estimate" a speed, without needing to specify from a scientific instrument
that you were doing 62 in a 60 zone, and can issue an infringement on that basis.
As with any other offence, that's called having "reasonable grounds to suspect..."