Ken Clarke in Thatcher's Resignation - Who are Solid Conservatives?

Maggie Thatcher Cabinet Colleagues Ouster Comments

'The Downing Street Years' Harper Collins hard back edition.

"Ken Clarke now entered. His manner was robust in the brutalist style he has cultivated: the candid friend. He said that this method of changing Prime Ministers was farcical, and that he personally would be happy to support me for another five or ten years. Most of the Cabinet, however, thought that I should stand down. Otherwise not only would I lose; but I would 'lose big'. If that were to happen the Party would go to Michael Heseltine and end up split. So Douglas (Hurd) and John (Major) should be released of their obligation to me, and allowed to stand, since either had a better chance than I did. Then the solid part of the Party could get back together. Contrary to persistent rumours Ken Clarke at no point threatened to resign."

What is this "Solid Part" of the Conservative Party, is this shorthand for what has become the clear enemy of our nation? Is it now led by David Cameron?