My husband and I have a good business idea, which involves using a named product and designing and producing a extra part (accessory) for it, in order to make it suitable for our (and others) requirements. We think that we would be able to sell the accessory (with our name on it) together with the original named product - with their logo on their product, as we are not trying to make their item look like it is ours.

Basically it is just an attachment to an already marketed product. Would we be allowed to do this, or do we have to inform the original manufacturers. We are worried that if we explain too much, they will just steal our idea.