I don't know how the MOD's claim that 'unidentified' objects cause no threat if they can't even identify them but I suppose they're just banking on people unquestioningly accepting it -there's some relevant reading at the link below concerning the work of British researcher Julian J.A. Hennessey and he does a good job of pointing out some of the 'inherent shortcomings' of MOD UFO policy including claims of 'force fit' debunking and massaging the statistics of actual unknown reports.
Secondly, judging from my correspondence with the Ministry, it appears unable to positively identify an extremely high number of the reports made. Yet the annual statistics never support this fact. UFOs listed as "probable balloons" suddenly become definite balloons statistically. Cases have even occurred where the Ministry was even unable to identify jet interceptors involved.
Thirdly, explanations given witnesses are often more puzzling to them than the nature of the UFO reported. In many cases, the witnesses, often trained competent observers, have regarded these Ministry explanations as an insult to their intelligence and certainly would never again report any other such observation to the Ministry. My discussions with airline pilots revealed that a majority of them would never make a report to the Ministry for fear of ridicule. A highly unsatisfactory situation caused by the present policy.
Fourthly, once an explanation has been given, the Ministry will not, even when the evidence has been presented to the contrary, review its findings if the evidence presented does not fit in with theirs. It has a strong tendency to ignore valid points in the statements of witnesses simply because it does not support what they think is the probable cause of the sighting.
Lastly, the Ministry only investigates the air defence implications of reports and admits that it has never carried out a study into their scientific implications. Scientists or serious UFO researchers have no access to these unclassified reports on file. Indeed, it is only over the recent years that such reports are permanently retained. Previously they were destroyed after a 5-year period.