There are estimated to be over two million EU nationals currently working in the UK, accounting for around 7% of the workforce, with over one million UK citizens living and working in other European countries. The ease with which EU citizens can come to live and work in the UK, and vice versa, is therefore likely to be a significant concern for employers, employees and expatriates whose access to skilled workers, jobs, healthcare and pensions could be impacted by a UK exit from the EU.

Under the principle of free movement, EU nationals have an automatic right to live and work in the UK, which could cease to apply if the UK withdraws from the EU. Whilst terms of withdrawal were being negotiated, there would not likely be any immediate change to the immigration rules given the obvious significant impact this would have for employers and employees; the position thereafter would depend on the model adopted for the UK's continuing relationship with the EU.

Membership of the EEA or an FTA model similar to Switzerland would be highly likely to require agreement to free movement of workers and therefore the position would remain largely as it is. However, if the UK reaches agreement on a different model not involving free movement of people, then it would become free to impose new migration criteria for EU citizens wishing to come and work here.

This could involve extending to EU nationals the current points-based system applicable to non-EU citizens. It has been suggested that around three quarters of EU nationals currently working in the UK would not meet the current Tier 2 General visa criteria applied to non-EU migrant workers, as they are either in insufficiently skilled roles and/or do not earn the required minimum salary (currently £20,800, due to increase to £30,000 in April 2017).This would obviously have a significant impact on sectors heavily dependent on low-skilled workers such as agriculture, manufacturing, hospitality, construction and healthcare, which would be likely to affect many regions, not only London and the South East. However, the Government would be likely to come under pressure to ensure the rules were adapted to avoid shortages.

Adopting the current system for non-EU citizens would also make it more difficult and expensive for multinationals to arrange cross-border secondments, which could have a significant effect on recruitment and retention of talent in sectors such as financial services and others. Short-term business travel to the UK could also become more problematic.

Of course, if the UK were to impose such restrictions, other EU countries would be likely to reciprocate in restricting UK nationals travelling to and working in their countries, a factor which the Government would have to bear in mind when approaching negotiations.

One particular pressure point would be whether any new restrictions were applied to UK and other EU migrants already living and working in a Member State other than their home state. It may be that reciprocal rights would be negotiated to ensure existing migrants were given the opportunity to seek indefinite leave to remain, but there are no guarantees.