Emerson, who is the Executive Director of The Investigative Project on Terrorism, subsequently issued an apology, telling the Huffington Post:

"I have clearly made a terrible error for which I am deeply sorry. My comments about Birmingham were totally in error. And I am issuing an apology and correction on my website immediately for having made this comment about the beautiful city of Birmingham. I do not intend to justify or mitigate my mistake by stating that I had relied on other sources because I should have been much more careful. There was no excuse for making this mistake and I owe an apology to every resident of Birmingham. I am not going to make any excuses. I made an inexcusable error. And I am obligated to openly acknowledge that mistake.
"Steve
"PS. I intend to make a donation to Birmingham Children's Hospital"

Despite the apology, Emerson still insisted London was patrolled by "Muslim vigilantes".

http://www.huffingtonpost.co.uk/2015...n_6452512.html