Mr Clark, former Defence minister and MP for Kensington and Chelsea, died on Sunday and was buried at a private family funeral before his death was announced.
In a statement issued yesterday, his family said that the maverick 71- year-old MP, famed for his acerbic and compelling diaries, had died after suffering from a brain tumour. Rumours of his ill-health had been circulating at Westminster since he had surgery three months ago for the removal of a suspected tumour.
Within minutes of the news of his death, it emerged that Mr Portillo, seen as the lost leader of the Thatcherite Right, would contest the seat at a forthcoming by-election.
As the by-election has to be called within three months, it is possible that Mr Portillo could be back as an MP before Christmas, positioning him perfectly for any challenge to William Hague.
Sources close to Mr Portillo, who lost his Enfield Southgate seat at the last election, said that he was "more likely than not" to apply for the seat.
In a highly unusual move so soon after the death of an MP, Conservative Central Office also confirmed that Michael Ancram, party chairman, would be "delighted" if Mr Portillo put his name forward to a shortlist of 12.
"William has always encouraged Michael Portillo to come back into Parliament as soon as possible. That's absolutely the position now," a senior source told The Independent last night.
Mr Ancram will draw up a shortlist that will be put to the Kensington and Chelsea Conservative Association and the local membership will then decide their final choice.
With a majority of 10,000, Kensington and Chelsea is probably the safest Tory seat and offers the former Defence Secretary the ideal chance of an early return to Parliament. Mr Portillo has been eyeing several London seats to contest at the next election.
Obituary, Review, page 6