The London skyline is seen from the Shard, the tallest building in the European Union, as the sun sets on March 28, 2017 in London, England.

Overseas companies that invest in the UK issued a flurry of warnings on Tuesday about the threat Brexit poses to their businesses, signalling their growing concern as the UK prepares to start the formal process of leaving the EU.

Forty European business lobbies, representing 20m companies in 34 countries, issued a statement calling for a post-Brexit settlement which would preserve the integrity of the single market, deliver a smooth transition and avoid creating "unnecessary" obstacles to trade and investment.