The extent and effectiveness of any loft insulation can often be easier to assess through an internal thermal imaging survey, or just a visual examination of the loft space.
The roof is the easiest escape route for heat if it is un-insulated, so the current recommendation for at least 270mm thick insulation may be one of the easiest ways to save heat.
There are a number of options for types of insulation, and while in many cases this may be a DIY job, there are some other factors to consider- see roof insulation page.
Photo and thermal image of loft hatch taken from inside the attic: the red areas show that the gap is leaking hot air into the cold the roof space.
Image of a stairwell of a house built in 2002. Investigation showed that the builders had failed to insulate the space between the ground floor and 1st floor under the integral garage- this resulted in un-vented air entering the cavity wall (stair wall) and floor space of two bedrooms. The blue areas at the edge of the stairs and along the bottom of the stair wall show that cold air is leaking into the house here due to the lack of insulation.