In respponse to the question Chris Galloway posted, that is the type of adaptor that I use. I also have a 13 amp adapter which you can buy from camping shops that has a 13 amp plug and connector for the circular plug.
Similar to the type that FTP posted.
But I always have an RCD in the wall socket.
My vacuum is a 3 motor 80 Ltr wet and dry, and I've had no problems running this, I also run a twin vaccuum three stage carpet cleaning machine from this extension, again with no problem and the draw of the carpet cleaner is far greater than my gutter vacuum.
All you have to remember is don't leave any coiled up bacause the excessive draw on the power it makes the cable act as a coil and will cause the outer sheathing will plasticise and eventually melt.