- Letters were given to almost 190 republicans suspected of crimes who had fled Northern Ireland
- They gave assurances that their recipients were not wanted by police
- The system was agreed between the last Labour administration and Sinn Fein from 2000
- In February, a case against 62-year-old John Downey fell apart when it emerged he had been given a letter in error
- In July, a judge-led inquiry found they were systematically flawed in operation but not unlawful in principle
- Northern Ireland Secretary Theresa Villiers has promised to clarify their status in the coming days
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The world's first ever 'hole in the wall' was installed in Enfield, north London, on June 27 1967.