Poland has warned British Prime Minister David Cameron against his plans to reform European Union migration rules to curb the number of arrivals, saying this was an "absolute red line".

Cameron last week unveiled proposals including delaying access to benefits for EU migrants for four years and deporting EU migrants if they have not found work after six months.

The proposals would require changing EU treaties.

"This is an absolute red line, that there is no discrimination on the grounds of nationality," Polish Deputy Foreign Minister Rafal Trzaskowski told BBC Newsnight late on Monday.

"When it comes to changing the rules in the EU, when it comes to social support and so forth, when it comes to undermining the existing laws, obviously we are going to react quite strongly," he said. "We are going to be against."

But he said that if Britain were to change its welfare system to make it contributions-based, "we then could talk about changes if they were absolutely non-discriminatory".

Cameron is under pressure ahead of a May 2015 general election as support grows for the UK Independence Party, which campaigns against mass immigration and for Britain to leave the EU.

Poles are among the largest group of EU nationals who come to Britain looking for work.

In his speech last week, Cameron said his proposed reforms were a "red line" for Britain and hinted that a failure to reform could imperil its European Union membership.

"If our concerns fall on deaf ears and we cannot put our relationship with the EU on a better footing, then of course I rule nothing out," he warned.