If the person's earnings (from self employment) are under £5075 per year the person can apply for a certificate of small earnings exception and not pay any NI contributions.
Even if they don't, their lack of NICs is unlikely to cause a problem. They'll get a letter telling them that they're behind with their contributions, but that letter specifically states that it's not a bill. It simply invites the person to bring their contributions up to date. Since you now only need 30 years of contributions to qualify for the state pension (which, apart from Maternity Benefit and Bereavement Benefit, is normally all that Class 2 contributions count for) a gap in contributions is extremely unlikely to have a detrimental effect.
http://www.hmrc.gov.u...ntro/selfemployed.htm
Chris