Negotiations over Britain's future in the European Union will ramp up in the coming weeks, David Cameron has said.
Leaders of some of the EU countries which back calls for reform of the 28-nation bloc have said they are yet to see details of the UK's proposals for change.
But the Prime Minister insisted talks are "going well" and said the pace will speed up in the coming weeks as he appeared at the Northern Future Forum summit in Icelandic capital Reykjavik.
Technical talks on Britain's proposals for EU reform have been under way with Brussels officials since June, and Mr Cameron will provide details of his proposals to fellow EU leaders in a letter to European Council president Donald Tusk early in November, ahead of substantive discussions between national leaders at a Brussels summit in December.
He said: "I would argue it's going well. I said I've launched the process and it's got under way. That was accepted at the June European Council. There was an update in October.
"Now, the pace will quicken with a letter I'll be writing to the council president at the beginning of November.
"But this is quite big changes that I think are necessary not just for Britain, but also for others in the European Union and, indeed, for those outside the European Union."
He added: "I'm confident we will make good progress and very confident after the discussion we had last night that we will take this forward and succeed."
The summit brings together leaders of northern European countries, including EU members and non-members.
Mr Cameron has warned that it would not be beneficial for Britain to follow the model of countries like Norway, which remain outside the EU but are required to make payments to Brussels and comply with EU regulations in return for access to the single market.
Former deputy prime minister Nick Clegg urged Mr Cameron conclude the negotiations early enough to give him time to make the case for continued EU membership to the public before the issue is put to a vote in the referendum promised by the end of 2017.
He told BBC Radio 4's Today programme: "I think it is very important that the Government as a whole has the time and the space to make the bigger argument to the British people, once it has got beyond the nitty gritty of the renegotiation."
Mr Clegg said that all of the models for relationships with the EU offered by non-member European countries like Norway, Iceland, Liechtenstein or Switzerland were "worse than being a full member of the single market".
"All of them involve a significant loss of control in which you have to abide by the rules of the EU but you have no right to write those rules, and furthermore you have to pay your dues, you have to pay money into the EU coffers," said the former Liberal Democrat leader.