Hi Johnnie
I too am in this exact same position and actually not that far from you Herts.
I was going through the do i hire, do i contract, do i sub contract, and every bit of research i do throws up new issues and complications.
Ignoring the fact of the new person, if you hire staff - you need to consider their actions will make you as a business liable. Anything from using a wrong image and getting sued by getty, or to making a coding slip that releases info - in short, you need to protect your business more, be it more insurance, and indemnity, or going ltd if your a sole trader.
In terms of the new person, its just not that easy. I have tried many sub-contractors (home and abroad) and never been happy with the results. Whether this is because i have stupid standards, or whether i am not a good boss/manager i do not know. In short always understand as posted above that they are turning up to just do a job, the business is your business and not theirs, and so their care level might not be as good as your own.
Moving on from that - i personally would recommend getting a free lancer to work in house on short term contract. This means you can limit your risk to a time period (wages) and if their skill or personality does not suit the end is always in sight.
If not, you going to have to start looking at PAYE which you might already do if your limited company, but guessing your a sole trader this might complicate your accounts a bit - may even drive up costs for your accounts a bit. Considering National Insurance contributions, too.
In short i have found it bloody hard to solve your problem and then end result was actually working harder and longer and being more selective about clients and projects. But this did not work, i ended up getting sick, giving away a few clients and currently running in “limited capacity” mode.
The big decision is really what do you “want”. If you want to expand and become an agency then costs will have to rise, you will have to learn or pay that accountant for the extra bits, and change how your business works. If your happy with you setup, then perhaps setting restrictions in place to limit your time issues might be a more sensible solution (i.e. book slots, and not take on too much - easier said than done for big clients though right!).
I know i have not been much help - as i have not been able to make this step either and suffered as a result of it. It is hard, but one i advise being careful and thoughtful about but make your decision on what is most important to you and then work out how to do it. (i.e. in my case “client satisfaction at a good job” rather than running myself into the ground!).
N