Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Allegations that a secret undercover police unit carried out spying operations on Labour MPs need to be investigated immediately, Nick Clegg demanded this morning. The Deputy Prime Minister said the idea that elected politicians were being 'snooped on' because of their views 'appalled' him and urged the Home Secretary Theresa May to order a wider probe into undercover police tactics to investigate allegations. It comes after a former officer, Peter Francis, said he read files on 10 MPs during his 11 years working for the Metropolitan Police's now notorious Special Demonstration Squad. The Deputy Prime Minister said the idea that elected politicians were being 'snooped on' because of their views 'appalled' himA former officer from a secret police unit admitted spying on Labour MPsTargets included deputy leader Harriet Harman, Peter Hain and Jack StrawNick Clegg this morning said the allegations, if true, were 'terrible'Deputy Prime Minister said a probe into police tactics to investigate them 
 Question:Hundreds of animal rights activists, neo-Nazi groups, campaigners for black justice and other campaigners who, unknowingly, were spied on by the _ could have their convictions overturned.

Special Demonstration Squad