Officials in both countries are hoping to agree a last-minute bilateral deal aimed at making the Brexit process less damaging for citizens in Gibraltar when the transition period ends on 31 December.
Spain’s proposed side-deal aims to preserve some free movement for people coming across the Gibraltan border each day to work in the EU.
“Talks between Spain and the United Kingdom over Gibraltar continue, but there too time is running out,” said foreign minister Arancha Gonzalez Laya.
“We won’t stop until the last second, but we expect in this game the active participation of the United Kingdom,” she told the radio station RNE.
The UK’s decision to leave the EU was very unpopular in the British overseas territory, where thousands of people cross the border with Spain every day for work.
Just over 95 per cent of the territory’s population voted to stay in the EU at the 2016 referendum.
However, UK officials are reportedly nervous about signing any side-deal on free movement that could be viewed as reducing British influence over the territory.
It comes as logistics chiefs continue to raise concerns about widespread disruption to the supply of goods in and out of the UK from 1 January.
British businesses are rushing to stockpile goods just five weeks before post-Brexit customs checks come into force – which is already pushing the cost of cross-border deliveries “through the roof”, industry sources have said.
Logistics companies said they have seen a surge in demand to bring goods into the country, and customs agents report being overwhelmed by pleas for help from traders navigating new rules for the first time.
“We have told our customers that the best thing you can do now is stock up, stockpile, and they’re bringing in as much as they can,” said Jon Swallow, director of Jordon Freight. “The consequence of that is there’s simply not enough capacity and the prices are going through the roof.”
Elsewhere, environment secretary George Eustice has revealed that the UK border potentially needs another 100 officials to deal with post-Brexit paperwork for food products.
Mr Eustice told MPs on Thursday morning that there are around 1,000 officers able to issue export health certificates for fish, although Westminster is working with its Scottish government counterparts to help fill a “gap” in Scotland.
“It is the case there are some concerns in Scotland where the Scottish government potentially has a gap in capacity of 100, we’re working with them to try to offer our help to ensure this gap can be filled.”
On Wednesday Michael Gove claimed the EU would be to blame if there’s border trading chaos in January because of its “rules are rules” approach.
The Cabinet Office minister also suggested there would be only “two to three weeks” of disruption. Speaking to the Logistics UK group, Mr Gove did admit there would “inevitably be some disruption”, saying: “Not everything will be alright on the night.”