UKIP leader Nigel Farage has pledged to make the Eastleigh by-election a four-way marginal fight and said his party's number one issue will be immigration.
Kicking off the party's campaign in the Hampshire seat vacated by Chris Huhne's resignation for pleading guilty to perverting the course of justice, Mr Farage said: "Our number one issue is that this country faces a second massive migratory wave
"We have nothing against people from Bulgaria and Romania, we wish then well, but we cannot think it's right this country has a total open door policy."
He said the pressure on housing, education and services from immigration "poses a major problem" for the country, especially if people from other countries claim benefits.
Citizens from Romania and Bulgaria will have full movement rights across Europe from 2014.