David Cameron will inspect efforts being made to strengthen the European Union's external frontiers on a visit to Bulgaria's border with Turkey.
The Prime Minister - who is considering whether the UK can increase assistance to support work to curb the flow of migrants - will see measures such as a newly-erected fence and beefed-up patrols.
Recent figures showed there have been more than a million illegal crossings of EU borders this year, as numbers have been dramatically swelled by refugees fleeing the violence in Syria.
That is 13 times the number seen in 2014, underlining the scale of the crisis engulfing the 28-member bloc - with large numbers arriving from Africa and the Middle East via Greek islands and Italy.
But some 27,000 have come in via the 150-mile border between Bulgaria and Turkey, a fact that Sofia believes has been overlooked.
Bulgarian premier Boyko Borissov joked that he wanted to give Mr Cameron "a geography lesson" to end his two-day visit - which was mainly focused on Mr Cameron's EU renegotiation drive.
Many European leaders had "forgotten that our border with Turkey and our sea border is longer than the border with Greece" , he told reporters after talks with the PM in Sofia.
Britain has already committed border officials to provide the equivalent of 60 months' work helping screen individuals arriving in Greece and Italy and is considering whether to expend that support.
That is not likely to cover Bulgaria, which has installed 21 miles of razorwire fencing to deter migrants - and plans another 62 miles - and has deployed up to 1,000 extra troops to the border.
The authorities have faced criticism from Oxfam over the alleged abuse of migrants - and one young Afghan man died, apparently the victim of a ricochet from a warning shot.
But the Bulgarian burden may be eased in part by an EU financial package to help Turkey absorb more of the migrants flowing over its border with Syria - towards which the UK has offered £275 million over the next two years.