KEEN to pack your bags and spend a bit of time living and working in the United Kingdom?

That traditional rite of passage is about to get harder than ever before, with a series of new anti-migrant policies announced overnight.

British Prime Minister Theresa May outlined her plan to dramatically scale back immigration at the launch of the Conservative party’s election manifesto on Thursday.

The policy will see the overall net migration lowered to “sustainable levels”, Ms May said — to below 100,000 annually.

But it could hurt the hopes of Australians looking to work in the UK.

“I want to see people here having the skills to take on these jobs, while still have a system that brings the brightest and best into Britain,” Ms May said at the launch in Yorkshire.

The change most likely to sting Aussies is the government’s plan to double the cost to companies employing migrant workers to £2000, or about AU$3500 per year.

That sharp rise will make the prospect of employing a foreigner less attractive to UK companies.

Some economists have expressed concern about the blunt black-and-white approach to immigration.

“In a global race for talent and innovation, UK firms risk being left in the starting blocks because of a blunt approach to immigration,” Carolyn Fairbairn, director of The Confederation of British Industry said.

Alexander Downer, Australia’s High Commissioner in London, has previously called for an easing of restrictions placed on Aussies in the UK.

The cost of foreigners accessing the National Health Service (NHS) will also rise to £600 (AU$1050) and visa requirements for students will be tightened.

If implemented, the changes would affect Australians who are already in the UK.

RELATED: Commonwealth Freedom of Movement Organisation wants free movement between UK, Canada, NZ and Australia

The flagged crackdown comes as new figures released this week show more Aussies are working in Britain than at any other time in the past 20 years.

In the first three months of this year there were 157,000 Aussies and Kiwis employed in the UK, an increase of 30,000 on the previous year.

Britons will go to the polls on June 8 and the Tories are expected to romp home with a healthy majority against Labour.