I have only seen the normal dowels which you help to support the cakes sold in the normal cake decorating shops in London. Where would I find the large dowel to drill through the centre? Does anyone know of any sites?

I buy mine at our "craft" type stores here in the US, or "hardware" type stores. I'm not sure if there are any sites that sell them.

How long are the dowels that you use for supporting your tiers? Here in the US we can get the real long (3' I believe) and cut them to size. They're just common wooden dowels that come in different widths.