Unfortunately the driver out yesterday received threats, the truck was vandalised and there have been several offensive complaints received."

A company representative also informed Mr Craig that people had made personal threats by email and over the phone which were "horrific", "violent stuff" and "the worst I have known". These had caused Adtrailers unilaterally to cancel their contract with GayMarriageNoThanks "to protect their staff". The violent threats and backlash to the campaign come just prior to the Third Reading of the Government's Marriage (Same Sex Couples) Bill in the House of Lords today.

The billboard campaign attempts to put children back at the heart of marriage in a debate which so far has "been about only the interests of adults," according to Mr Craig. The group also delivered a letter to the Prime Minister yesterday in Westminster, enclosing a copy of the New Family Structures Study by US Professor Mark Regnerus.

The study, which drew upon randomly-selected sample of nearly 3,000 respondents, show that children are "most apt to succeed well as adults - on multiple counts and across a variety of domains - when they spend their entire childhood with their married mother and father."

Mr. Craig believes the incident with the billboards raises serious concerns in light of the same sex marriage Bill. "These incidents show how free speech is already being shut down before any change in the law on marriage" he said.

"The billboard was simply intended to initiate legitimate debate concerning the best environment for raising children. We're quite convinced that the overwhelming evidence demonstrates children do best with their married birth mother and father. This is a debate which urgently needs to take place.

"Vandalism, abuse and threats of physical violence threaten to shut down such democratic debate. Advertising companies and others will no longer be willing to carry 'controversial' pro-children and pro-family messages if the safety of their employees is put in jeopardy.

"The situation will only get worse with the passage of the same sex marriage bill. What will Mr Cameron do about it? We have been asking him to consider the welfare of our nation's children. Now we're also asking him what he will do to ensure freedom of speech for those who, for very good reasons, oppose same sex marriage."

END