Leaving the European Union would curb investment in the infrastructure sector in Britain in the two years after the referendum and possibly for longer, credit rating agency Standard & Poor's (S&P) said on Wednesday (18 May).

S&P said the forecast was based on the result of a survey it conducted among industry members in the lead-up to the referendum on 23 June, which will determine whether Britain will remain part of the 28-country bloc.

"It is said that perception is reality, and based on what investors are telling us, the reality is that a Brexit scenario could put long-term funding for UK infrastructure at risk," said S&P global ratings managing director and head of infrastructure research, Michael Wilkins.

Currency volatility was cited as the major short-term concern for infrastructure investors, while 50% of the 51 respondents mentioned political instability and a turbulent macroeconomic environment as the main threats.

However, fewer than half of those who took part in the survey believed that Britain would vote to leave the EU next month. Despite the concerns surrounding the outcome of the referendum, a certain degree of uncertainty could have a positive influence on the market, Wilkins added.

"The uncertainty introduces risks for both domestic and foreign investors, and therefore concerns for debt financing and credit quality," he said. "But these risks also mean that opportunities for capturing higher returns arise, which could ignite some unexpected activity in the sector."

However, S&P indicated that from a ratings perspective it was yet to see direct implications for stand-alone credit quality in the infrastructure sector from a potential vote to leave or from any volatility in the aftermath.

"The worries about political instability and macroeconomic turbulence are unlikely to directly impinge on investment, but rather postpone decisions to make investments, as investors stay on the sidelines until the UK-EU relationship is renegotiated or until the economy settles down," it said in a statement.

"Yet, this may be a shorter-term phenomenon, which our survey results also suggest. One explanation could be that investors may leave the market in the short run, and re-enter once they have more visibility or see increased opportunities for higher yields."