Was the UK General Election 2015 was Rigged? (Poll)Watch
There have been many past allegations of voter fraud (especially surrounding postal voting) in particular constituencies. There's been a long history of it in Northern Ireland and lots of controversy about it in inner city areas of England with high ethnic minority populations.
The issue of government-level interference in the process is generally considered to be a non-runner, but some people have investigated allegations in this area. The election before Tony Blair took power, when John Major was returned to office against all expectations, was a particular focus of enquiry as it seemed he was very certain about being returned in an odd way. Some people accused the authorities of widescale rigging, but the allegations were never properly investigated.
Simultaneously gutted for, and angered by, Cambridge.
EDIT: obviously it wasn't rigged.