I did this some years ago.
I employed someone to work for me when I got too busy to cope with new clients. I rented my room within another business at the time.
The paye and paperwork was not too difficult and I got a lot of help on how to do that from HMRC or Inland Revenue(whatever they were called at the time!).I also got some funding for her salary for the first few months from a government agency so that woiuld be worth looking into if you are going down this route.
The pros to having an employee are ;
The control !
You set their hours, and what products get used and can ensure their is a uniformity of service.
Cons:
paperwork
Holidays and holiday pay
Employee rights
minimum wage
An employee has loads of rights (rightly so) which you would need to know about, and they really need to be bringing in at least 3 times their wage to make it worth your while.
If they are not busy you still need to pay them, and you need to set aside money for their holiday pay.
I found it a big responsibility being responsible for someones livliehood, and yet some weeks when we had been really quiet, she was taking home a larger wage than me
I still would think it would be better than getting in a self employed person as what would the legalities of you subletting a room that you already are sub letting?