It is feared a long-running dispute between the U.K. and Spain over the tiny British territory of Gibraltar could arise during a state visit by the Spanish monarchy to London on Wednesday.
Spain's King Felipe and Queen Letiza started their engagement to the U.K. on Wednesday, meeting Queen Elizabeth II and Prince Philip -- who will soon retire from public duties.
It is the first state visit to Britain by Spanish royals in 31 years. The last such visit from Spain was made by King Juan Carlos I and Queen Sofia in 1986.
The Queen and King Felipe are expected to discuss historic, cultural and commercial ties between the two countries, as well as Brexit.
However, some local media report British lawmakers being wary of Spanish attempts to raise sovereignty issues regarding Gibraltar.
Gibraltar, a British overseas territory on the southern tip of the Iberian peninsula, has been a source of tension between the two countries for years.
With a population of around 30,000, Gibraltar was ceded to Britain by Spain under the treaty of Utrecht in 1713. In referenda held in 1967 and 2002, the Gibraltarian public widely rejected proposals for it to be governed by Madrid. Spain, however, continues to press its claims to the territory.
Spain earlier this year agreed to the EU's ruling on Brexit negotiations that "no agreement between the EU and the United Kingdom can be applied to the territory of Gibraltar without an agreement between the Kingdom of Spain and the United Kingdom".
King Felipe, in a UN address in March, asked the U.K. to "end the colonial anachronism of Gibraltar with an agreed solution between both countries to restore the territorial integrity of Spain".
The Spanish royals will attend a gala dinner at Buckingham Palace on Wednesday evening and are expected to address both Houses of Parliament on Thursday.
