Earlier this week, Attorney General Dominic Grieve warned MPs that it would be a "serious matter" if Britain defied the European Court of Human Rights' ruling.
While Parliament was entitled to retain the current ban, he said that it could leave Britain liable to pay compensation as well as legal costs and expenses.
– Dominic Grieve, Attorney General
Parliamentary sovereignty remains, it is open to Parliament to decide not to change the law.
However if Parliament chooses not to implement the judgment this would be a serious matter because it would place the UK in breach of its international obligations to which it is a signatory.