It is "childishly simple" to register bogus voters in UK elections, a human rights body's investigation suggests.
There have been problems with postal votes
The Council of Europe's report said the British voting system was "open to fraud", particularly with postal votes.
Its inquiry was prompted by a complaint from Tory MP David Wilshire, following concerns about fraud in local elections in Birmingham.
It acknowledges that reforms have blocked some loopholes. The government said UK elections were "free and fair".
Since the UK introduced postal and proxy voting on demand in 2001, there has been a series of allegations of vote rigging - a judge looking into Birmingham's 2004 local elections said he had heard evidence of fraud that "would disgrace a banana republic".
Mr Wilshire, a member of the British delegation to the council, had accused the government of "systematically ignoring" pleas from the Electoral Commission and of failing to put its "house in order".
The report said it was "childishly simple" to register bogus voters, then use postal ballots to commit electoral fraud without detection.
It blamed this partly on the way voters are registered without having to give details like their date of birth or National Insurance number.
The council recommends that identifying data should be checked on all postal ballots, and these should no longer be handled by party activists.
In a statement the Ministry of Justice said no election could be guaranteed to be "fraud-free" but measures had been put in place to increase security in UK elections.
It said "significant steps" had been taken to tighten up security and help police and prosecutors in tackling electoral fraud in the Electoral Administration Act 2006 and other legislation.
"Importantly, we have introduced a system of personal identifiers for postal voters to ensure postal votes cast at an election are valid," it said.
"We have seen the success of these measures in a reduction in the number of allegations of fraud and any proven instances of fraud are still extremely rare."
It added it wanted to take a "proportionate" approach to protect the integrity of the system, while making it easier for more people to vote.