Tony Blair has criticised people who held parties to "celebrate" the death of Baroness Thatcher, saying they were in "pretty poor taste".
The former Labour prime minister urged critics of his Conservative predecessor to "show some respect".
The comments come after parties took place in several cities to mark the 87-year-old's death on Monday.
A Labour source also said that leader Ed Miliband "categorically" condemned such behaviour.
Lady Thatcher remains a hate figure to many on the left, having privatised several state-run industries and been involved in long run-ins with trade unions, most famously during the miners' strike of 1984-5.
Parties were held in several parts of the UK on Monday night, including in Bristol, London and Glasgow. Several police officers were hurt during violence in Bristol.
Mr Blair, who, like Baroness Thatcher, won three general elections, told the BBC: "I think that's pretty poor taste. You've got to, even if you disagree with someone very strongly - particularly at the moment of their passing - show some respect."
He added it was "part of modern political life" to make "very difficult" decisions.
Mr Blair also said that "when you decide you divide and that's just the way of it" and that Lady Thatcher would be "pretty philosophical" about any criticism following her death.
A senior Labour source said: "Ed Miliband categorically condemns any celebration of Lady Thatcher's death. As he made clear yesterday she was a huge figure in British politics and on the world stage.
"While the Labour Party disagrees with much of what she did, we can respect her personal achievements."
It is expected that many Labour MPs and peers will pay tribute to Lady Thatcher when Parliament is recalled from its Easter recess for this purpose on Wednesday.
But John Mann, who represents the former mining community of Bassetlaw in Nottinghamshire, said he would not attend, adding: "I would have done it on Monday when Parliament reassembles. I do not know why we are wasting taxpayers' money on an additional session.
"It is perfectly valid that, when a prime minister dies, MPs can pay tribute, but this could be perfectly properly done on Monday."
Respect MP George Galloway, who once represented Labour, also said he would not attend, calling it a "state-organised eulogy" rather than a "debate".