Who are your customers? If they are businesses being VAT registered from the start may be useful. On the other hand, if your customers are consumers, only registering when you have to might be better. The VAT registration limit is currently £85,000 a year - that's a rolling 12 months. You might want to register for VAT if you have incurred a lot of costs or are going to in the set up phase so you can recover the VAT you're charged by your suppliers.
Your profile indicates that you are an agent. What sort? You need to make sure you take advice to make sure that you are able to deal with VAT issues for agents correctly.