As has been noted in earlier posts - there is much concern that a major boundary review is to completed before the next election, on the basis of an electoral register that misses a large number of people entitled to vote. The following written question and its answer have been published in Hansard
Mr Blunkett: To ask the Deputy Prime Minister what steps he plans to take to seek to ensure 100% electoral registration; and if he will make a statement. 
Mr Harper: The Government will be considering what steps can be taken to improve registration rates in the context of the implementation of Individual Electoral Registration in Great Britain.
The Electoral Commission Report, "The completeness and accuracy of electoral registers in Great Britain", published in March 2010, reported that the registration rate in the United Kingdom was 91-92% (based on figures from 2000). The report also found that: "there was a decline in registration levels from the late 1990s to 2006. The same evidence base suggests that the registers have stabilised since 2006, although it is likely that the completeness of the registers has declined since the last national estimate in 2000."
The report also says the process of estimating registration rates is an "imprecise science" and says that "All current approaches to estimating the completeness and accuracy of the electoral registers at a national level are imperfect", but that "The completeness of Great Britain's electoral registers remains broadly similar to the levels achieved in comparative countries."