The head of the UK Independence Party has promised to slash net igration into Britain by 90 per cent as he unveiled an election poster showing escalators riding up the White Cliffs of Dover.

In a campaign stop at the ferry port city, Nigel Farage accused Prime Minister David Cameron of being "dishonest".

Farage says his party's immigration policies would stop half a billion people have access to a UK passport through EU residency.

UK correspondent Gavin Grey told Newstalk ZB's Andrew Dickens the anti-EU party's popularity is starting to slip.

"They've been riding on a tide of quite popular success, although that is beginning to dwindle a little bit."