Mr de Klerk's first admission that efforts to lure the right-wing into accepting a negotiated solution to the country's problems have all but failed is certain to dominate talks due in Downing Street today between John Major and Nelson Mandela, president of the African National Congress.
'The whole process of negotiation is under enormous pressure at the moment,' Mr de Klerk told a National Party congress last night in Stellenbosch. 'It would be no exaggeration to speak of a crisis in the future.'
'Crisis' in the less polite language of the right-wing, which includes Mangosuthu Buthelezi's Inkatha Freedom Party and Afrikaner separatists, means civil war.
This is what they have been threatening should the government and the ANC go through with agreements reached in multi-party talks to draw up an interim constitution in November, to pave the way for elections on 27 April for a five- year coalition government.
Yesterday afternoon Mr de Klerk met with all the right- wing leaders opposed to the deal - Chief Buthelezi, General Constand Viljoen of the Afrikaner Volksfront, the Conservative Party leader, Ferdi Hartzenberg, and the rulers of the Bophuthatswana and Ciskei 'homelands', Lucas Mangope and Oupa Gqozo. The five came together last week under a new banner, the Freedom Alliance - an odd assortment of bed-fellows, as their rivals have noted, united more by their fear of an ANC government than by a common vision of the future.
Chief Buthelezi, for example, says he seeks a non-racial, federal solution while General Viljoen, a former armed forces chief of staff, demands a sovereign Afrikaner state within whose boundaries resident blacks would be deprived of political rights.
The latter option, which Chief Buthelezi would seem now to endorse, is categorically rejected by Mr de Klerk - as it is by Mr Mandela. An indication of how unsuccessful the South African President's talks with the Freedom Alliance yesterday had been was provided just hours later by Mr de Klerk's words to his party congress. If the right were not brought on board within four weeks, he said, 'another plan' would be required. 'As a democrat, I believe that there is no better instrument than a referendum,' he said.
The referendum option has been discussed in political circles for some months, the logic being that it provides Mr de Klerk and Mr Mandela with a trump card against the right-wing. Chief Buthelezi claims to represent 'the Zulu nation'. General Viljoen and Mr Hartzenberg claim to represent 'the Afrikaner nation'. Opinion polls have cast grave doubts over these propositions - and have ridiculed similarly large claims by Mr Mangope and General Gqozo.
The Freedom Alliance as a whole fear a referendum because they realise that not only would the thinness of their purported support base be exposed, it is certain that the combined ANC and National Party vote would guarantee a large majority for a 'yes' vote.