You can get a special junction box designed for lighting, the standard ceiling rose is a junction box as well as holding the cable supplying the lamp, some times you can swap the three connection block for a 4 connection block and get it to fit, I have one where I have even got a load capacitor to fit inside the shell for the new lamp, but it depends how much room you have.
Google Ashley J501 16 Amp Downlighter Junction Box and see if that helps.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!