BRITAIN: Shadow foreign secretary Mr Michael Howard insisted the prospect of British entry was now "a dead duck" - and former Europe minister Mr Keith Vaz urged Prime Minister Mr Tony Blair to begin campaigning or lose the argument by default.
But No 10 said nothing had changed, and could not point to any forthcoming events Mr Blair would use to sing the praises of the single currency.
Observers expected that a Yes vote in Sweden would have added momentum to calls for a referendum in the UK.
The third non-member of the euro, Denmark, also voted No in a referendum in 2000.
Mr Vaz said the Swedish referendum result was a "bitter blow" to single-currency campaigners in the UK.
He warned Mr Blair that he should start promoting the case for the euro, or risk the campaign being "over before it's begun".
Mr Vaz, who was Europe minister between 1999 and 2001, said: "The Swedish euro referendum result was a bitter blow to the pro-euro campaign in Britain.
"The main lesson to learn for the Prime Minister and the government is that they have to put into deeds the good words they have said about being pro-euro."
Mr Blair's spokesman said: "The Swedish referendum is a matter for the Swedish people, and of course the government respects their decision. It would have respected it whatever decision the Swedish people had made. But it does not affect own policy on the single currency.
"We are clear and have been clear throughout that the government will only recommend joining if the economic case is clear and unambiguous. The national economic interest will be what guides this government in whatever decision it takes."
After Chancellor Mr Gordon Brown announced that his five tests for euro entry had not been met earlier this year, No 10 said a "roadshow" would boost the benefits of the EU and campaigners hoped that would include the benefits of the euro.
But No 10 said no events were planned.
Mr Howard said the No vote in Sweden indicated that the euro was a "dead duck".
He told the BBC: "I am pleased for the people of Sweden and I hope that the lesson which will be drawn in this country is that people will realise that the question of whether Britain should join the euro should be seen for the dead duck that it is."