This is a fairly loose thing to say. Firstly no the UK doesn't have a judicial system. There are separate legal systems in England & Wales, in Scotland, and in Northern Ireland.

Amongst many other issues, The Post Office has a historic freedom to investigate, pursue and prosecute criminal cases on its own behalf- no need to persuade e.g. the police. This has been shown, for anyone with any doubt, to be a massive conflict of interest. Another repeated occurrence is the discovery that the Post Office claimed, but would not provide evidence and used this 'position' to bully people into accepting plea bargains. Essentially the Post Office dishonestly and deliberately abused its position in numerous cases to bypass the legal system in each of the home nations so that defendants would simply turn up in court to plead guilty and be sentenced. Had these cases been required to meet the standards of a conventional criminal investigation and trial in any of the UK home nations, many more of them would have failed to convict.