Before the 1999 House of Lords Act, the Conservatives had a large in-built majority in the House. The problem of the Lords being able to veto all government legislation if it was so minded is covered by the so-called Salisbury convention.
The convention (sometimes called the 'Salisbury doctrine') states that the Lords will not vote down a Bill that seeks to enact a manifesto pledge on which a government was elected. In this way, the Lords submitted to the popular mandate of the Government of the day, regardless of its party.
More recently, since the removal of the hereditaries, there is some discussion as to whether the convention should hold. Some argue that the legitimacy of the Upper House was enhanced by the 1999 Act, allowing it a wider veto, while others maintain that, without elections to the Upper House, the convention should remain unchanged.