British Prime Minister David Cameron has hailed the first same-sex marriages in England and Wales as sending a “powerful message” about equality.

The law changed on Saturday after midnight, with a number of gay couples vying to claim the title of being the first to be married in Britain by trying to time it perfectly so their vows were said just seconds after the clock struck 12.

The prime minister said the reform was necessary because “when people’s love is divided by law, it is that law that needs to change”.

Writing in the gay news service, Pink News, he said “this weekend is an important moment for our country” because “we will at last have equal marriage in our country”.

Mr Cameron, who has faced opposition from some in the Conservative Party about his backing for the change, said: “This is something that has been very important to me.

The prime minister said he had been extremely lucky “the most incredible lifelong partner” in his wife Samantha.

“Of course any marriage takes work, requires patience and understanding, give and take – but what it gives back in terms of love, support, stability and happiness is immeasurable.

“That is not something that the state should ever deny someone on the basis of their sexuality. When people’s love is divided by law, it is the law that needs to change.

Congratulations to the gay couples who have already been married – and my best wishes to those about to be on this historic day.

— David Cameron (@David_Cameron) March 29, 2014

“The introduction of same-sex civil marriage says something about the sort of country we are.

“It says we are a country that will continue to honour its proud traditions of respect, tolerance and equal worth.”

The Marriage (Same Sex Couples) Act came into force in July last year but it was not until March 13 this year when couples were able to register their intention to marry under the Act.

While whoever says the words “I do” first can claim the title of first gay couple to be wed in the UK, other couples who previously married abroad have already had their unions recognised.

On March 13, the law in England and Wales changed to recognise same-sex marriages performed overseas.

Rainbow flags will be hung all over the country to celebrate the occasion, with one flying at the heart of Westminster.

Scotland has also legislated to allow same-sex marriages, with the first ceremonies expected to take place later this year.