Michael Portillo is to stand for the leadership of the Conservative Party.
He said the responsibility for two "catastrophic" election results lay with all members of the party.
Unless changes were made, the party would "go further down", he said.
The shadow Chancellor said the Conservative Party believes in tradition and history, improving public services, emphasising the duties and rights of people and supporting the stability of families.
He said the party needed to be "moderate and understanding" and "internationalist".
Under his leadership, the Conservative Party would work closely with other centre and centre right parties in Europe. This would allow the party to oppose Britain joining a single currency more effectively.
Attracting people from a broad range of society to the party would also play a major part in the Conservative's standing over the next four years, he said.
It was also announced that Francis Maude would lead Mr Portillo's campaign.
Eleven members of the shadow cabinet have so far declared their support for Mr Portillo.
They are Peter Ainsworth, Edward Garnier, David Heathcoat-Amory, Oliver Letwin, Andrew Mackay, Francis Maude, Tim Yeo, Gary Streeter, Archie Norman, David Willetts and Theresa May.