Mr Diamond has advised the couple not to appeal the decision, saying that it would be "futile".
"The courts are so set against religious freedom for Christians that an appeal is likely to only make matters worse," he said.
Instead, he and the Johns are seeking a political intervention to ensure that Christians can live and work according to their conscience.
A petition is being submitted by campaign group Christian Concern on their behalf. It warns that recent equalities legislation and its interpretation in the courts has led to several Christians being barred from different areas of public life and employment, contrary to freedom of conscience.
This, the petition says, is "creating a serious obstacle to the Christian community's full and active involvement in the Big Society initiative".
"We call on the Prime Minister to act decisively to address this situation, securing the change necessary to ensure that the law provides a basis for widespread involvement in service society whilst properly upholding the dignity of every individual, including those who seek to live with integrity to Christian conscience and teaching," it reads.
The group is lobbying MPs and peers in the House of Lords to seek a review of the Equality Act.
Mr Diamond said there was much to be commended in the Equality Act and the Sexual Orientation Regulations and that sexual orientation or faith should not be a reason to discriminate against others.
However, he said the laws were "poorly drafted" and "leaving too much to the discretion to the Courts".
He added that they were being used to "eradicate Judeo Christian morality and usher in secular values".
Mr Diamond said the "countless" cases where accommodation of conscience was being denied to Christians amounted to a "liberal tyranny".
"In recent years, there has been a combination of bad laws and a number of poor judicial appointments by the previous Government," he said.
"Where there are excellent judges they are restricted by bad laws.
"Unfortunately, there are also judges making law based on personal predilections. Parliament must remedy this situation as a matter of urgency."
He continued: "Coerced morality or coerced immorality, depending on one's perspective, is not the hallmark of a free society.
"In all too many instances, the attempt by Christians to seek justice in the courts is a barren experience, almost as if a special animosity is reserved for adherents of this faith."