2010 UK Parliamentary General Election Interim Report: Review of problems at polling stations at close of poll on 6 May 2010 - Electoral Commission. According to the commission at least 1,200 people lost their chance to vote on election night because of bad planning by councils
The Guardian datablog has a useful spreadsheet of places where the electorate couldn't vote.You can donload it directly from the website.
The OSCE ODIHR also deployed a mission to the Uk elections - some preliminary needs assessments are currently online.
In response to the elections Institute Public policy research has published a report Devising an Electoral System for the 21st Century: The case for AMS