The number of flights between the UK and Spain could collapse by 95% if no Brexit deal is agreed, the air travel industry’s global trade body has warned.

Travel for tourists, business and cargo will all be significantly affected in a “no deal” scenario, according to a report prepared for the International Air Transport Association (Iata), which represents 290 airlines around the world.

The route between Spain and the UK is particularly at risk because of the size of both markets, as well as the large volume of tourist traffic between the two countries. IATA figures show there are currently 5,052 UK-Spain flights a week.

Alexandre de Juniac, Iata’s director general and chief executive, warned that a no-deal Brexit could lead to “thousands, millions of passengers” potentially grounded at airports after the UK leaves the EU on 29 March 2019.

“If nothing is done it will be a nightmare in the European and UK airports,” he said.

The EU and the UK’s Civil Aviation Authority have plans for a “bare bones” agreement to ensure a basic level of service, according to the report, which was compiled by the consultancies Taylor Airey and Frontier Economics.

However, the British government has repeatedly emphasised that a no-deal Brexit is possible, leaving significant uncertainty and the possibility of a breakdown in talks.

Airline travel is currently governed by a complex patchwork of different regulatory regimes covering issues such as safety, security and immigration controls. The former Brexit secretary David Davis committed the UK to leaving the European Common Aviation Area and all other EU-negotiated agreements.

Major British carriers may also be unable to continue transatlantic flights if there is no deal, Iata added.

International Airlines Group, the owner of British Airways, as well as Virgin Atlantic and Norwegian UK, could be ineligible to carry out transatlantic flights. Ownership of those firms is currently spread across the EU, meaning they could fall out of the scope of any separate UK-US agreement.