Prime Minister Gordon Brown has told Portugal that as EU president it must respect all the UK's "red lines" as the new EU treaty is finalised.
Mr Brown (right) inherited the British negotiating stance from Tony Blair
The UK wants to retain control over human and social rights, foreign policy and tax and benefits.
Mr Brown was speaking to reporters after talks with Portuguese Prime Minister Jose Socrates in London.
He told Mr Socrates that the UK wanted its negotiating objectives "reflected in all the detail of the agreements".
Portugal aims to turn the defunct EU constitution into a Treaty of Lisbon.
Mr Socrates would like to do that by October, to enable him to focus on other business.
He has dismissed the idea of member states, namely Poland, seeking fresh concessions during talks on wording, which are due to start on 23 July.
The new treaty framework agreed in Brussels preserves much of the planned EU constitution, rejected by Dutch and French voters in 2005.
Reform of the EU treaties - signing by December
Start of regular EU-Brazil summit
First EU-Africa summit for seven years
Getting Turkey's membership talks "back on track"
Ensuring European consensus on Kosovo
Co-ordination of employment policies
But the constitution's envisaged post of "foreign minister" was dropped in favour of a "high representative" for foreign policy and a reform of the EU's voting system was delayed until at least 2014, to placate Poland.
Both Mr Socrates and Mr Brown face calls from their respective oppositions for a referendum on the planned treaty.
The line taken by Mr Socrates and Portugal's president - although he is from an opposition party - is that there can be no talk of a referendum until the text emerges.
Mr Socrates said fighting terrorism would be a priority during Portugal's EU presidency.
His other priorities include an EU-Africa summit to be held in Lisbon in December.
Portugal has close ties with its former colonies but is also cultivating its near neighbours in North Africa and countries further south through the African Union, whose summit Mr Socrates attended last week.