This length of black leather-cloth is sufficient to cover the internal A-posts, dash top rail and dash lower rail on any Mini with a centre speedometer (lacking the moulded plastic fascia introduced on the Clubman). These are very tricky areas to close-trim with material because of their complex curvature- the job really needs to be undertaken with the front screen and dash trim removed from the car, using plenty of evenly applied contact adhesive on well prepared areas. It may be appropriate to find an experienced local body shop or trimmer to undertake this job for you if you do not feel confident enough to tackle it yourself.
These areas were always originally covered on the original Coopers, otherwise on standard cars they were normally visible as bare painted areas of the body pressing. The idea was perhaps to eliminate glare from the glossy paint, and it did lift the interior by adding a subtle touch of refinement.