Cardinal Keith O'Brien said the majority of politicians had supported a number of attacks on human life with "apparent lack of reproach from conscience".
His comments came two weeks after MPs voted in favour of plans to allow scientists to carry out research on human-animal hybrids and rejected moves to cut the abortion age limit from 24 weeks.
Speaking at a Mass in the House of Commons crypt, the religious leader said tonight: "It has struck me that for all the Church's calls for recognition of the inviolability of conscience, the sad reality is that the vast majority of politicians have given support to various attacks on human life with apparent lack of reproach from conscience.
"What does one say then, in the face of those who without guilt condemn the innocent in the womb, show disregard for family life and play God with the building blocks of life?"
Cardinal O'Brien, the Archbishop of St Andrews and Edinburgh, pointed to newspaper claims that abortions in Scotland have soared to a record high, with 13,703 procedures carried out last year.
The religious leader told MPs and members of the House of Lords that we live in a confusing time of "great moral challenges" as he stressed the need for legislators to follow their consciences, even at the expense of political difficulty.
He added: "We cannot but help notice that consciences among even some who ostensibly see themselves as loyal Catholics or champions of the life have been dulled even so far as to acquiesce with what is euphemistically called a right to choose."
The cardinal has been an ardent campaigner against the controversial proposals for embryo research, claiming they would lead to experiments of "Frankenstein proportions".
He posted a video on the YouTube website, setting out his opposition to legislation contained in the Human Fertilisation and Embryology Bill, which would allow scientists to create human-animal embryos.
"The possibility of a mixing up of human life and animal life at its beginnings, this quite simply is abhorrent to us as Catholic Christians," he said on his web broadcast.
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