Tony Blair has decided to delay naming the date for the general election for 24 hours because of the Pope's death.
Tony Blair's plans have been put into 'mild disarray'
The prime minister had been expected to ask the Queen on Monday to dissolve Parliament ready for a 5 May poll.
But BBC political editor Andrew Marr said Mr Blair has told aides he no longer thinks the timing of the news would be appropriate.
Instead, Downing Street says Mr Blair will attend vespers at Westminster Cathedral in memory of John Paul II.
He will also lead tributes to former Labour premier James Callaghan in Parliament.
All the main political parties suspended national public campaigning for Sunday and Monday as a mark of respect for the Pope.
Cabinet ministers and Labour organisers had been preparing for an announcement on Monday following a planned visit to Buckingham Palace at 1000 BST.
Mr Blair is now expected to announce the election campaign on Tuesday morning.
He is also likely to attend the Pope's funeral in Rome towards the end of the week.
Monday: Vespers service in memory of the Pope and Parliament's tributes to James Callaghan
Tuesday: Prime minister expected to ask Queen to dissolve Parliament and announce a 5 May poll
Wednesday: Last prime minister's questions
Thursday: Possible last day when Parliament sits
Friday: Royal wedding
Monday: Parliament formally dissolved
Andrew Marr said Labour's plans had been thrown into "mild disarray".
In a statement, Downing Street said: "The prime minister will be attending vespers at Westminster Cathedral tomorrow afternoon at 4.30pm.
"In response to speculation we can confirm that he will not be going to Buckingham Palace tomorrow."
Monday 11 April is the deadline for dissolving Parliament for a 5 May poll.
If the election is called next week the government will rush to get its remaining legislation through Parliament.
MPs and peers are likely to stop sitting on Thursday, with Parliament formally dissolved the following Monday.
That schedule would leave Friday clear for the royal wedding of Prince Charles and Camilla Parker Bowles.
Ahead of a hectic parliamentary week, Home Secretary Charles Clarke has already admitted controversial plans for identity cards and a new offence of incitement to religious hatred could be dropped.
It is not the first time Mr Blair has needed to change his election timetable. In 2001, he postponed the election because of the foot-and-mouth epidemic.