Judges should not be influenced by other branches of government and should be absent of any bias. Without effect check on government tyranny may result and government could discriminate against individuals or groups
Arguments for its independence
Security of tenure: judges cannot be removed from office based on their decisions
Rule of sub judice: contempt of court for any servant of the government to attempt to interfere with the result of a court case
Since 2005 appointments largely independent
judicial salaries can't be cut and are strict on public rules about what expenses may be claimed
Arguments against judicial independence
Judges are specifically selected by the government to ensure decisions are friendly to the government
Government might use the pay to influence
Ministers are becoming increasingly more willing to make public statements about courts and express opinions on the stances the judges have taken. E.g. May criticised the courts devision to ignore rules aimed at deporting foreign criminals