Migration Watch UK said Commonwealth immigrants who have not qualified for British citizenship could "significantly influence" the next General Election if voting is close.
Chairman Sir Andrew Green said:
One example is that a student visitor from a Commonwealth country planning to study for six months would be allowed to enrol on the electoral register and vote in a parliamentary election if one was held during the duration of his or her stay.
This is clearly absurd. The issue is one of basic fairness.
If people want to participate in deciding the future of our country they should at least become citizens.
More top news
Proposal would see a task force set up to assess environmental impact from breaches of emissions testing rules.
Hundreds remain missing in what is becoming one of the worst natural disasters to hit Central America in recent years.
Medical charity worker relates how he and colleagues tried to save patients and staff following devastating air strike.