By Ollie Stone-Lee
BBC News political reporter
It was one of Westminster's more tuneful demonstrations, said one police officer as evangelical groups belted out hymns in protest at planned religious hate laws.
Passions - and songs - ran high at the protest
"They've been singing quite happily, it's very pleasant," mused the officer.
Indeed, the beltway opposite Parliament seemed to have transformed into a gospel choir stall in the shadow of Westminster Abbey.
"Stand up, stand up for Jesus, ye soldiers of the cross;
Lift high His royal banner, it must not suffer loss," they sang.
And with it, a sea of banners from about 400 protesters were lifted high, bearing such slogans as: "the blood of Jesus Christ", "the holy spirit and fire" and "woe unto them that decree unrighteous decrees".
In other words: MPs, watch out.
'I am not ashamed'
The protest brought together some unusual bedfellows - religious believers waving bibles and confirmed atheists - to sing, almost literally, from the same hymn sheet.
They believe the planned new offence of incitement to religious hatred, which is being debated again by MPs, will threaten free speech.
Stand Up, Stand Up for Jesus was in the protest's repertoire
Democratic Unionist MP Sammy Wilson proclaimed to cheers and hallelujahs how Christianity had spanned 2,000 years and did not need protection from Tony Blair or his new legislation.
"People are queuing up to use this legislation to stop people preaching what they want," he said.
His DUP colleague Willie McCrea declared: "I do not care what man says, I am not ashamed of the Gospel of Christ."
He went on to lead the demonstrators in a chorus of Amazing Grace.
'Identity at stake'
Emotions ran high among the protesters.
Moses Ahumah, 40, who lives in east Acton, London, but originally comes from Ghana, was worried his freedom of speech would be constrained if the legislation was passed.
"I would feel a heathen, my identity would be taken from me," he said.
"I believe I am created to express myself and feel that is being taken from me."
MP Willie McCrea leads a rendition of Amazing Grace
The Reverend Richard Blyth, from Hither Green Baptist Church, in Lewisham, London, said the laws were both ludicrous and dangerous.
People can only be found guilty of the new offence if they intend, or are reckless about, stirring up religious hatred.
But Rev Blyth said: "The question of intent is discerned not by what the speaker says but by what the hearer deems that they heard.
"Therefore it is possible for hearers who feel that they are insulted to go the police and say a particular speaker or group of speakers is trying to stir up hatred against them."
On a day of unlikely alliances, the National Secular Society's Stewart Ware explained how he was able to make common cause with the evangelists.
"We do not agree on many things but we do on this," said Mr Ware, 52, from Walthamstow, London.
Surrounded by religious chants and songs, the campaigner against religious privilege confessed: "It is slightly odd and I won't say I enjoy it 100% but it's an experience.
"It's basically about freedom of speech. No one has the right not to be insulted or offended."
A few yards away, Yemi Odubanwo, 47, from Hackney, London, said the legislation would prevent people preaching "righteous beliefs".
Now the demonstrators must await Parliament's final judgement.