Nissan alone employs 6700 in its Sunderland factory with at least another 13,000 employed in the supply chain. Much of the money those people earn is spent locally in shops, pubs, restaurants and other businesses, thus providing work for many more.
Logistics would become much more complicated if the UK were to leave the EU, because Nissan is currently able to switch production and supply its customers without having to bother too much about paperwork and export/import tariffs. Nissan is one of the North East's (and UK's) biggest exporters. There's a very real possibility that it would relocate, if the UK leaves the EU. The North East is beginning to establish a worldwide reputation for engineering (eg Hitachi's new train-making plant), so it would be tragic if this is knocked off course.