If I say I’m the driver on the part 1 of section 172 form does this mean I am self incriminating myself for the offence & stopping my defence, as I do not know who was driving the vehicle at time & date of offence as it was a long time ago?
If you name yourself as the driver then yes you are giving the police evidence that they can use against you. Having said that you are still free to defend yourself on the basis that you don’t accept that you were speeding.
If you don’t know who was driving at the time of the alleged offence then you should not nominate yourself. You would then have a defence if you could show that you have used reasonable diligence to figure it out or if it has not been reasonable practicable due to the passage of time and it happening a long time ago.