Airbus has warned it could leave the UK if the country exits the European Union single market and customs union without a transition deal. The European planemaker said the warning was not part of "project fear, but its "dawning reality", BBC reported on Friday. Airbus employs about 14,000 people at 25 different sites in the UK. Last week, the outgoing president of the Confederation of British Industry (CBI) said sections of UK industry faced extinction unless the UK stayed in the EU customs union. It brings together the EU's 28 members in a duty-free area, with a common import tariff for non-EU goods. British Prime Minister Theresa May has ruled out staying in the customs union. The UK is due to leave the EU on March 29, 2019. In its Brexit "risk assessment" published on Thursday, Airbus said if the UK left the EU next year without a deal - meaning it left both the single market and customs union immediately and without any agreed transition - it would "lead to severe disruption and interruption of UK production". "This scenario would force Airbus to reconsider its investments in the UK, and its long-term footprint in the country," it added. The company, which makes wings for its passenger planes in the UK, also said the current planned transition period which is due to end in December 2020 was too short for it to make changes to its supply chain. As a result it would "refrain from extending" its UK supplier base. It said it currently had more than 4,000 suppliers in the UK. The warnings from Airbus echo comments made on Wednesday by the boss of Siemens in the UK. J\u00fcrgen Maier said the UK should remain in the customs union after Brexit unless there was a "proper alternative". Last week, Paul Drechsler, the outgoing president of the CBI, said some parts of industry in the UK faced extinction if the country left the EU customs union. Paul Drechsler said car firm bosses had come to him saying the industry would suffer unless there was "real frictionless trade". Drechsler also said there was "zero evidence" that trade deals outside the EU would provide any economic benefit to Britain.