The Voodoo AC receptacle is a standard Hubbell IG8300 rated at 120V. It is not code for use in the UK, that is why it will not fit in the box. If you want an audio grade receptacle that will fit in a UK box and be to code, try the Furutech FP-1363-S.
http://www.furutech.com/2013/02/02/1856/
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http://www.furutech.com/2013/02/02/1856/
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