The UK Border Agency is responsible for border control for the United Kingdom, enforcing immigration and customs regulations.
The Ministry of Justice is responsible for the justice system - the courts, prisons and probation services.
Directgov has all the information you need on how to apply for a passport or identity card.
The Independent Police Complaints Commission is responsible for ensuring that complaints about the police are dealt with effectively.
The Home Office is the lead government department for immigration and passports, drugs policy, counter-terrorism and police.