This is the kind of people that has the right to search and interrogate you. In a case of mistaken identity Lance Corporal Mark Aspinall is savagely beaten by British police. (This is a November 2008 video)
You are asked to let British police and Mi5 to have access to your private data under the disguise of protecting you. But who protects you from their abuse when they have all the power?
The most shocking of the ordeal that this war veteran had to go through is that he actually got charged and convicted of assaulting the police!
If you are ever arrested by the police do not let them bully you into talking, they can not force you to talk. You have the right to remain silent, you say nothing until you have talked to your solicitor first.