Plus one for NFU. Also try your local High Street Brokers - such as Swinton - they will phone around for a number of quotes.
You will probably find it hard to arrange business insurance online. I have always found most websites want me to phone for a quote.
Be honest with the broker about exactly what you are doing. There is no point trying to get the premium down if it leaves you uncovered. If you are selling mugs or safety clothing it is best to get product liability as well.
Do you have to insure the premises as well?