Class 4 NIC - Overseas self employment

A client of mine has just returned from 9 months in Australia. Whilst he was there he undertook self employment and I am now completing his self assessment tax return. Due to the short duration of his visit overseas he has remained a uk resident throughout. Clearly he is liabie to tax in the UK, but what about Class 4 NIC? The self employment only took place in Australia - he was an employee before he left the UK and upon his return - no element of his self employment took place within the UK.

Appreciate any answers

Thanks