Sir Paul Coleridge, who founded the Marriage Foundation, was speaking after a heterosexual couple lost their Court of Appeal bid to have civil partnership opened up to them too.
Charles Keidan and Rebecca Steinfeld (above) say they don't want to get married, but want a legal recognition of their relationship. They also say they are deeply disappointed by the Court of Appeal's ruling.
The couple plan to appeal today's decision to the Supreme Court if able.
Currently only homosexual couples in the UK can become civil partners. In other European countries heterosexual civil partnerships exist as an alternative to getting married.
Speaking on Premier's News Hour Sir Paul Coleridge said: "If couples have some kind of principle objection to getting married but nevertheless want to make a very serious commitment, they should be facilitated to do that.
"Whatever can be done to encourage people to take these decisions seriously and in a thoughtful way should be done, and we get into a dangerous area of worrying too much about labels and not enough about substance."
But Sharon James from the Coalition for Marriage welcomed today's ruling.
She told Premier: "The gold standard of commitment is marriage; with the declarations made in the presence of witnesses and the expectation of lifelong faithfulness... civil partnerships just don't offer that.
"If you did bring this in you'd be providing a rival institution to marriage... and I believe that's only going to weaken marriage by creating a two-tier system, offering a sort of marriage-light option."
Listen to Premier's Alex Williams speaking to Sir Paul Coleridge on the News Hour:
Listen to Premier's Aaron James speaking to Sharon James: