Can border checks between Gibraltar and Spain be reintroduced?

Short answer

Yes, in limited circumstances. Following the Schengen Borders Code, controls can be temporarily reinstated where there is a serious threat to public policy, public health or internal security, initially for 10 days and potentially extended up to six months.

Detailed answer

The Treaty applies Schengen rules on the temporary reintroduction of internal border controls. Controls may be reinstated for an initial 10 days, extended by a further 20 days and then in monthly periods up to a maximum of six months.

The Treaty also allows a party to seek temporary release from its obligations, in which case border controls between Gibraltar and the EU would return a week after notification, and either the UK or the EU may terminate the Treaty on 12 months' written notice.