Right ok.
VAT
You can register for VAT any time you like. If you have a VATable turnover of more than £60k (I think) they you are required to register for VAT.
The benefit of registering for VAT when you dont have to is that you can claim the VAT back on all of your inputs (i.e. your expenses). The downside is that you have to charge VAT on all of your outputs (i.e. your sales). For customers who are not VAT registered, this means a price increase of 17.5% (as they cannot claim it back). If your customers are VAT registered then they will not suffer at all. Therefore the key thing is to determine whtether your customers are VAT registered or not. The other factor to take into account is how many of your expenses have VAT on them.
National Insurance
As soon as you start earning money from a self employed business you are obliged to let HMR&C (Her Majesty's Revenue & Customs) know that you are doing so. You will have to pay Class 2 NIC (£2.10 week) - usally set up by direct debit. You will also be liable for Class 4 NIC. However, if you are paying sufficient Class 1 NICs with your normal employment, then you can apply for an exemption from the majority (I think) of Class 4. (Class 4 is based on your earnings, in the same way as Class 1).
Income Tax
AT the end of the tax year (to 5 April) following when you notify HMR&C of your new status they will send you a tax return. This si nothing to be scared of!
It has to be submitted by the following 31 January. However, if you would like HMR&C to calculate the actual tax due, the return has to be submitted by 31 September.
The return is generally self-explanatory. In fact I have heard it said that it is easier to follow if you know nothing about income tax!
You can pay a local accountant (probably around £300, maybe less) to compltete the return for you.
I hope this helps somewhat.
