The two new chapters relate to freedom of movement, in Chapter 2, and the right of establishment and freedom to provide services, in Chapter 3.
A Montenegrin government source told BIRN that the Britain was the only EU member country blocking Montenegro; all other member states had reached a consensus on allowing Podgorica to open the two chapters.
The Foreign Ministry declined to comment on the alleged blockade when asked by BIRN about London's concerns over Montenegro’s accession.
It said the British embassy in Podgorica should be asked why its government was blocking Montenegro. The UK embassy also declined to comment.
Montenegro has already opened 24 out of its 35 negotiating chapters, including the most challenging ones, on the rule of law, judicial reforms and the fight against organized crime and corruption.
In April 2015, Montenegro said it was ready to open negotiation in Chapter 3, after the European Commission approved a negotiating position for this area a year earlier.
"Freedom of movement" means that all citizens of EU countries can move to, or reside, study or work in any other EU member country.
However, Britain is deeply opposed to the principle, claiming an unprecedented influx of EU workers has undermined wage levels and pushed UK-born workers out of jobs.
However, since Britain voted to quit the EU in a referendum on June 23, the future of the European project has distracted and preoccupied EU leaders, to the disadvantage of prospective members.