Does a patrol car can send NIP without pulling you over if speeding

[arrav]

Was wondering if a patrolling car can issue a NIP through post when they have plenty of time to stop me.
I am sure i haven't speeding, however i jumped lane at a round about and entered yellow box.
And also doing 40ish when it is 40 and just using the limit.
I wasn't worried but at junction when waiting for traffic lights i saw the police looking at me.
So this crossed my mind have i done anything wrong or will i get a speeding ticket or any

 

[arrav]

Thanks for your swift response, bit relieved
Say if I have speeded without my knowledge, can patrol car can send speeding ticket home?

Thanks in Advance

 

[arrav]

Thanks once again everyone for your time and valuable inputs.