I should add that another factor is that, so far, the UK has tested only just over a quarter of a million people for Coronavirus, and will certainly never test everybody in the UK -- so, again, there is a lot of information that can only be modelled, or estimated, rather than known. Confirmed cases stand at a little over 50,000 today, and that is likely to represent a smallish fraction of the actual total, maybe at most a tenth.
People can't lie about what they don't already know. Every country is in this position, to some extent or another. The possible exceptions are countries whose Governments are not accountable directly to the people, or to "strong man" governments: North Korea, China, Brazil, Belarus and a few others. For the rest, incompetence and ignorance are far more likely explanations than malice for any gap between what we are told is happening and what actually happens.