My mum was Gibraltarian and I still have family living there.
There have been several referenda as to whether Gibraltar should remain British, the overwhelming response has always been 'yes'. The people are British citizens and have no wish to become Spanish.
To those who have asked, English is the official language but all Gibraltarians are bi-lingual, speaking both English and Spanish.
Spain has tried to bully Gib over a period of many years, this is just the latest example and was entirely expected by everyone except, it seems, the British government. As a previous poster upthread said, prior to joining the EU which forbids the restriction of movement, there were long periods during which no-one was permitted to cross the border, flights to Gib were denied access to Spanish airspace and so had to go round and take longer, water had to be shipped in tankers via Morocco during periods of drought, fishing vessels in British territorial waters were harassed. Even now, the queues to cross the border are horrendous as cars are searched inch by inch and individuals are body searched, all done deliberately to make the process as painfully slow as possible. They can't at the moment stop people crossing the border but they make it as difficult as they want.
What Spain would really like to see is the closure of the airport. The water supply is now secure so that is no longer a point of leverage.
The whole idea is, and has always been, to try and isolate Gibraltar and its people so that they give in and ask to become part of Spain. I wouldn't be surprised if Spain closed the border on the day the UK officially leaves the EU.
Gibraltar has had to deal with all of this before, and, if necessary, will do so again.
The whole thing is a just an example of how the UK now stands in relation to the EU; prior to Brexit, the EU took no sides over Gibraltar as both the UK and Spain were members of the EU. Now that we are leaving, the EU will actively support the claims of its member state, ie, Spain.
This is just the beginning. We will see this stance again and again over the coming years; the EU will fight hard for and prioritise its member states in all negotiations, be they on trade, finance or diplomacy.
Would the UK give up Gib in order to negotiate a trade deal with the EU? I would hope not,and the government say not, but the temptation must always be there. Historically, Gib was strategically important as it's positioned at the gateway to Mediterranean and so could, and did, control shipping movements in and out of the Med. This became less important with the advent of nuclear weapons and the military presence decreased, but in the current climate in the middle east, who knows?
Just another one of a series of bargaining chips in this sad and sorry process.