I have found a suitable solution to the question I asked earlier. To do this I used the Convert Geometry Type function from MMQGIS plugin (the plugin must be installed). MMQGIS → Modify → Convert Geometry Type From the window I chose the layer(line type) and chose New Geometry Type (this has several options) I used Centroid and selected the Output Shapefile. The result is a shapefile of the centre points of all the lines with all the attributes from the original file. (Point to note, if a line is curved, the centre point will not appear close to the line).