Anyone wondering whether this is an isolated incident should read this:
http://news.bbc.co.uk/1/shared/bsp/hi/pdfs/judgment.pdf
It is the full judgement on the Lutfur Rahman affair where that gentleman was thrown out of office (as the Mayor of Tower Hamlets) and banned from standing for five years. This was because of widespread fraud and malpractice (in various guises) in the mayoral election of 2014.
It is a bit heavy going but worth a read if you can manage it. It explains some of the extraordinary goings-on that took place during the run up to that election and on polling day.
Since then there have been other, albeit less serious, reports of similar activity in other areas with a heavy Asian population.