Ashers bakery's 'gay cake' case could go all the way to the European Court of Human Rights if it were to lose its appeal at the Supreme Court, its backers indicated yesterday.

Five Supreme Court justices sat in Belfast for the first time for two days of complex legal arguments that came to an end last night.

The judgment is not expected for several weeks but if it loses the case, Ashers could take it to Strasbourg, its supporters said.

Ashers baking company is a Northern-Ireland based firm run by the McArthur family. It refused to bake a £36.50 cake for a LGBT activist Gareth Lee because he asked for the slogan 'Support Gay Marriage' to be put on it.

The McArthurs said that went against their evangelical Christian belief but they were held to have discriminated against Lee and ordered to pay £500 in compensation. That verdict was upheld in the Court of Appeal and now the case has reached the Supreme Court. 

The court heard the McArthurs were being forced to act against their beliefs. 

Their barrister, David Scoffield QC, told the supreme court: 'This is a case of forced or compelled speech, unlike other cases which have come before the court.

'Mr and Mrs McArthur have been penalised by the state in the form of the judgment at the county court for failing, through their family company, to create and provide a product bearing an explicit slogan – "Support Gay Marriage" – to which they have a genuine objection in conscience.'

But Lee's barrister, Robin Allen QC, said he was bearing a 'heavy burden' because of the protracted legal battle. 

'This is what was a relatively small incident in his life which has become enormously significant and continues to be so,' he said. 'That is a heavy burden to bear for one individual.'

The McArthurs are backed by The Christian Institute, a Newcastle-based conservative campaign group, and spokesman Simon Calvert said: 'The Christian Institute has agreed from the start that we will meet the entire legal bill for the McArthurs,' he told journalists outside court.

'We and our supporters are very happy to do that for them because of the stance they have taken.

'We will wait and see how much it is going to cost for the hearing here in the Supreme Court.

'The Supreme Court will take months to issue their ruling. When that ruling comes down, the McArthurs will want to sit down with their lawyers and see whether they have won, whether they have lost, whether it's a partial victory – because that is entirely possible in a case like this – and consider their options from there.

'Anyone who has exhausted their domestic remedies is free to go to the European Court of Human Rights. However, whether the McArthurs will want to do that is a decision for another day, and obviously depends on the ruling that the court gives, whether they win, lose or a bit of both.

'No-one is foolish enough to predict what eventually the judges will do. We are absolutely confident that the McArthurs have a very strong legal argument and a very strong legal team, but whether the Supreme Court will be persuaded is a matter for them.'

Lee is backed by the Equality Commission in Northern Ireland, a public body set up in 1998, which is paying Lee's legal fees.

Chief commissioner Michael Wardlow described him as the 'ghost at the banquet'.

'He has been living this for four years, and the media and others have been focusing on the McArthurs,' he said.

'He is sitting at the side of this, and he has been having to live each day seeing that this still has not finished.

'I don't know how you would feel if you walked into a shop and had to try to understand what is the conscience of people providing the service... do I have to go through a list before I can be served? And I think this is hopefully going to settle it once and for all.'

Gay activist Peter Tatchell defends Ashers bakery in 'gay cake' case 

Peter Lynas, Northern Ireland director for the Evangelical Alliance, said 'discrimination laws protect people, not messages'.

'This case has been portrayed as a battle between gay rights and religious freedom; it is actually about compelled speech and conscience. It has implications for everyone and that is why it is so important,' he said.

'The notion that a Christian can practise their faith on Sundays but must forget it on Monday is not real freedom of religion and certainly not freedom of conscience. Biblically, work is an act of worship, a place in which Christians express their faith.'