The performance of British firms, which rely on most of their sales in European markets, deteriorated after the country voted to leave the EU in 2016, according to newly compiled data.

A survey of the 100 largest companies on the London stock exchange, which generate more than 50% of sales within the EU, showed that their collective average price performance fell by 3.3%, a study by FactSet for MarketWatch showed.

For companies that generate less than 50% of sales within the EU the difference was starktheir collective average prices jumped 47%. FactSet uses the current composition of the EU, which includes the UK.

The data highlights the multinational composition of the UK’s leading firms index, with companies such as GlaxoSmithKline

GSK, 0.86%

Unilever

ULVR, 1.52 m%

and Reckitt Benckiser

most of their sales are outside the EU

In addition, the FTSE 100 industry analysis (TICKER:UKX) shows that the consumer, financial, telecoms and utilities industries are likely to be vulnerable to Brexit. This is because all these industries have 50% or more of the EU’s revenue exposure and not enough of the FTSE 100 as a whole.

The data firm also searched for the term Brexit in the conference call transcripts of the 67 FTSE 100 companies that conducted midyear earnings conference calls between June June and 14 September. Of these 67 companies, 27 cited the term Brexit while talking to the financial and consumer services industry recording the highest number. However, FactSet did not specify whether Brexit was called a positive or negative impact by these firms.

John Butters, senior revenue analyst at FactSet, said: “a Look at the FTSE 100 index as a whole shows that companies, regardless of industry, with large revenues in the EU and UK, have failed to deliver since the Brexit vote.

Next year, China’s economy is expected to grow more slowly than the Eurozone, not to mention the US and China. The mix of Brexit and General economic uncertainty is getting better, he said.

The survey found that two-thirds of institutional investors believe that leaving the EU without a deal on October 31 will have a negative impact on global markets, while 31% expect serious consequences.

However, if the sun strengthens the agreement before the deadline, 71% of institutional investors expect it to have a positive impact on the markets.