Former presidents Nelson Mandela, Thabo Mbeki and FW de Klerk, and former deputy presidents Phumzile Mlambo-Ngcuka and Baleka Mbete, are among those affected by "serious budgetary constraints" being experienced by President Jacob Zuma's office.

The Times can reveal that the former top politicians were over the past two weeks notified that their travel and subsistence allowances for the rest of year have been cut but would resume in the new financial year, which starts in April.

The two-paragraph letter, headed "Benefits of Executive Office", reads: "The Presidency is currently experiencing serious budgetary constraints and unfortunately the budget that was allocated to you for travel and subsistence has been exhausted. We are therefore not in the position to fund any further flights until 31 March 2012. This benefit will resume with effect 1 April 2012."

The policy of executive benefits allows former presidents and deputy presidents an unlimited number of journeys on scheduled commercial domestic flights.

Yesterday, the offices of both Mbeki and De Klerk confirmed that the former heads of state had received letters notifying them of the temporary cancellation of their benefits, but they refused to elaborate on how this would affect them.

Mbeki's spokesman, Mukoni Ratshitanga, said the development would "obviously impact negatively on the former president's programme, as indeed on other similarly situated officers".

"He has received the letter from the Presidency and so he accepts what the Presidency has got to say. It is not as if he has a choice about it," said Ratshitanga.

De Klerk's personal assistant, Brenda Steyn, confirmed that he received the letter on Wednesday.

Mlambo-Ngcuka's letter, dated November 9, was signed by the secretary of the cabinet on November 14.

Mlambo-Ngcuka is in the UK and is not aware of the cuts.

Nelson Mandela Foundation spokesman Sello Hatang said he was not in a position to comment.

A senior government official yesterday questioned the cuts, describing them as "quite a bizarre situation".

"Was the money exhausted on Zuma and all his wives? The Presidency needs to explain what happened to the budget," said the official. He added that some ex-presidents still did state-related work supported by the allowance.

Presidential spokesman Zanele Mngadi said last night that the cuts had been necessitated by the economic climate and that staff have been told to reduce expenditure.

"The Presidency is also exploring economy class travel for senior managers up to chief director level as part of the cost-saving measures. All units within the Presidency have been informed about cost-cutting measures and they have all accepted what is now called inside the Union Buildings the 'financial diet'.''

She said it was "grossly misleading" to suggest that Zuma's spouses were considered a serious cost factor as the spousal unit was a "very tiny component" of the Presidency and was also participating in the cost-cutting campaign.

In September, Zuma was accompanied to New York by both his wife Thobeka Madiba and fiancee, Bongi Ngema-Zuma, to attend a session of the UN General Assembly.

In March last year it was revealed that taxpayers would spend more than R15-million on supporting Zuma's three wives and some of his 20 children for the 2010-2011 financial year.

The travel cut comes six months after Mbeki was forced to take four different flights to reach war-torn Sudan after charter flights, paid for by the Presidency, were withdrawn.

In February, the Sunday Times revealed that the Presidency was unhappy about Mbeki's travels to Sudan. An internal memo said they were costly, "unsustainable" and "will require some changes".

The government spent more than R20-million on 11 charter flights for Mbeki's Sudan missions between April 2009 and October last year.