Later today, former Prime Minister John Major will warn an audience in Germany of the consequences of a split between the UK and the rest of the EU.
Speaking to the supporters of German Chancellor Angela Merkel's Christian Democrats in Berlin, he is expected to describe the two parties as being "close to a breach that's not in our interests or theirs".
While pointing out that the UK is not opposed to the principle of free movement, he will say it is unable to continue accepting the number of EU migrants arriving in the country at their current rate.
He will emphasise the importance of the bloc helping the UK to limit immigration into the country, since otherwise it will fuel the case for leaving the EU. However, he warned earlier this year that leaving the EU would leave the UK isolated.
Current Prime Minister David Cameron has pledged to hold an EU membership referendum in 2017 if he is unable to renegotiate the UK's position in the bloc before then.
Cameron has faced sharp criticism from MPs who believe independence would be economically detrimental to the UK, but Major has previously said he believes Cameron will succeed in reclaiming powers from Brussels before the referendum date arrives.