Nino UK only
Copied from reply to me previous post*
Prolific support can you provide any reassurance to those who have already provided their number?
DO NOT give your NI number to anyone, apart from your employer and that includes Prolific.
Prolific are not your employer and there is a massive risk of identity fraud and you will get no sympathy of anyone if you are scammed.
The UK Govt. are the ones saying this not me, so supply it are your own risk, but do not cry to a Govt. agency or the Police when the brown stuff hits the fan, because believe me they will have no time for you.