Exports of U.K.-built vans, trucks and buses rose 11.6% in the first half to 43,782 units and, with almost all of the output headed to the European Union, the industry is concerned.

The U.K. and mainland Europe vehicle-manufacturing industries are highly integrated, with both vehicles and parts moving seamlessly across borders. Any Brexit-related changes to tariff and non-tariff barriers or regulatory and labor issues will hurt the sector’s competitiveness.

Society of Motor Manufacturers and Traders figures show 63.5% of commercial vehicles built in the U.K. were exported, with 27,818 units headed to 45 countries.

Post-recession growth in the EU has bolstered U.K. CV manufacturing, as evidenced by a 13.8% rise in demand from the region and 94.7% of U.K.-built CVs headed there so far this year.

All 24,447 British vans and 62.9% of trucks exported in the first half were destined for EU fleets.

Israel topped the list of largest markets outside of the EU, taking 1.2% of U.K. exports, followed by Australia (1.1%), Hong Kong and Taiwan (both 0.6%) and New Zealand (0.4%).

The EU remains by far the biggest trading partner for U.K. -built CVs, but the iconic British bus is stamping tickets all over the world. Some 53.6% were destined for Asia, 35.1% headed to North America and 11.0% traveled the 10,000 miles (16,100 km) to Oceania.

“With almost every British-built van and truck destined for Europe, this reiterates the critical need to secure a new trading relationship that ensures this important sector can remain competitive,” SMMT CEO Mike Hawes says in a statement.

With the U.K. and European vehicle manufacturing industries so highly integrated, a beneficial relationship will take time to negotiate, Hawes says. “This is why we need government to seek an interim arrangement that will maintain our place within the (EU) single market and customs union until this can be achieved,” he says.