The item you need is called an omni-bounce diffuser. This is a small plastic dome that fits snugly over the flash tube of your Canon Speedlite, Nikon Speedlight or various other units. It turns your flash into a bare bulb effect light source. Luckily, you can pick up an omni-bounce to fit your particular flash for less than £4.99.
The other item you’ll need is a silver tin foil roasting pan. These come in various sizes, but we are looking at the kind of size that would be used for roasting something like a turkey with reasonably high sides. Trace the outline of the omni-bounce in the centre of the pan. Slide the pan onto the omni-bounce and secure it with some duct tape. You’ll then need to cover the top surface of the omni-bounce with foil to stop light escaping out of the top of the dome.
You want the light to be emitted from the sides into the foil dish and then thrown forward. The entire assembly can be attached to the flash. This is another one that does not look pretty, but you’ll be surprised how effective it can be. As an alternative, instead of the silver foil pan, you can try the very cheap white disposable plastic bowls used at parties.