Bit of a pandoras box this 1-technically you should make him paye but as a small 1 man band company this may not be practical for you financially, you could continue paying him normally as a self employed opperative although this leaves you open to possible financial losses later when hmrc investigate you & would deem his emoyement status under current legislation as wrong which would make you liable for not only his NICs contribution but your contribution of his wages as well!!!.
Self employment loopholes are being closed all the time as the gov wants everyone in the construction industry to become paye- but due to the transient nature of our work & verying sizes of companies employing operatives is very difficult to police but eventuallyeven the SME companies will be audited- @ the moment you could contact a payroll company such as hudson contracts,where for a small weekly fee legally the operatives self emoyment status can be maintained by working for them on a temporary contract & they then supply there labour to you via that company- may sound complicated but tbh only a couple of forms.
