Looking to hire designer for a few days. What do I need to know?

I'm probably going to hire a freelance web designer for a few day to complete a project. The designer will probably be freelance so I will be paying a fixed amount on completion. Are there any legal issue such as tax details I need to be aware of. Also should we be signing any documents, for example a requirements list to state the conditions for completion of the job. Thanks

Edit: I live in the UK

From experience I can say that it is always a good idea to establish a contract for these kinds of agreements. Even if this is for a short period of time. Even if the one you hire is a friend. A contract:

• Makes it clear for both parties what each is expecting from each other (sometimes you think it is very clear, only to find out the other party had something totally different in mind)
• Provides more assurance to both of you that the other one will come through. Legally, things are also clearer if they are put in writing.
• Often you forget about certain things if you don't work out the details and just start working. By using a contract, you remember to state the payment terms or define in what format you want the products to be delivered, for example.

You should use a written contract, which you both sign, and in it specify what needs to be delivered, the criteria for success, the payment schedule and the procedure for dispute resolution.

There should be no tax implications, as you are hiring a professional and not engaging in an employer-employee relationship.