If the UK is going to go to war with Spain over Gibraltar, I hope there's a referendum. Personally, I don't want any of my money going to defend an anachronism.
Of course Gibraltar wants to remain British. It's a 1950s theme park with red letter boxes and fish and chip shops, which doesn't pay taxes to the UK. It's a tax haven and offshore gambling HQ, which undermines the EU. Spain is welcome to it.
Fallon, Howard and Davis are talking nonsense. The UK has no realistic chance of hanging on to Gibraltar by traditional defence methods. The only reason that Gibraltar's been kept on the back burner is because Spain and the UK are/were members of the EU and there were political pressures to maintain the status quo.
If mainland Brits care so much about Gibraltar, they really should have thought about it before the referendum.