evidence: Anti-Brexit campaigners erected six mock customs checkpoints along the Northern Ireland and Irish Republic border on Saturday, in a protest over the possible impact to peace, jobs and the free movement of workers. Northern Ireland, a British province, will be the only land frontier between the United Kingdom and the European Union once Britain leaves and some fear that will mean a return to checks at the border where about 30,000 people cross each day for work. The frontier was marked by military checkpoints until a 1998 peace deal ended three decades of violence between Catholic nationalists seeking a united Ireland and Protestant unionists who wanted to keep Northern Ireland British. More than 3,600 died in that time.