Sadly I have to charge VAT as I turn over enough to make Customs and Excise sit up and take note
You cannot charge VAT unless you are VAT registered - you can register voluntarily if your taxable turnover is under £61000 per year. If your taxable turnover is over £61000 per year then registration is compulsory.
As for laws regarding a DJ, there are none - but there are laws, bylaws and regualtions that you need to be aware of.