The Director of Public Prosecutions, Sir Ken Macdonald, said too many cases had been rejected in the past but there was now a greater emphasis on making sure there were trials.

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The usefulness of the e-mails may also strengthen the hand of those who, like Sir Ken Macdonald, formerly Director of Public Prosecutions, want Britain to admit domestic intercept evidence in court, as many countries do.

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After a two-month investigation, Scotland Yard detectives handed over a file to the then director of public prosecutions, Sir Ken Macdonald, who announced in May 2007 that he was recommending Mr Lugovoi be charged with murder.

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