OK please remember this is guess work but here is what I would suspect. I would think the previous owners had a nice light they wanted to keep so go a cheap one to replace it with.
However in many houses the ceiling rose not only acts as a point to hang the lamp from but is also a junction box.
If yours is a new house it will have brown and blue cores. If so, where I say red change that to brown and where I say black change that to blue.
In this there are four connections. Forget about earth people normally get that right which leaves three connections and either two or three cables giving two or three reds and two or three blacks.
The latter blacks is where we get problems. Assuming you have the same number of red and black wires one of the blacks should have a sleeve on it and should feed the brown wire on the fitting.
If this wire has lost it’s sleeve and have been put with the other black/s then when the light is switched on it will blow fuse.
Often they connect the reds to the lamp as well which is wrong so when light switch is off lights still work. The reds only connect to each other they do not connect to lamp.
So if this fault has been there since you bought the house that’s what I expect. If this seems to ring true look at
http://www.ericmark.talktalk.net/lights.htm which may help you.
If however the lights were working OK then stopped one will look for something which has hit the wires. Cables should run horizontally or vertical from switches the latter more common but often this is not the case. And if one looks you can normally find where a shelf or picture has been put on the wall and hit cable below. Also flooring the loft often either traps wires or hits them and moving items around in the loft can be the last straw.
I hope that gives you a few pointers
Eric