Gross domestic product is forecast to rise by 2.2 percent this year and 2.3 percent in 2017, similar to growth in 2015 and down from forecasts of 2.5 percent for 2016 and 2017 made in December.

"The UK's economic performance is reasonably good when measured against our main competitors, but it's only mediocre when compared against long-term trends," BCC acting director-general Adam Marshall said.

Other forecasters have made similar downgrades since the start of the year, and economists polled by Reuters last month on average forecast growth of 2.2 percent in 2016 and 2017.

The BCC urged Chancellor George Osborne to use next week's annual budget statement to boost investment in transport and digital infrastructure, and made no mention of Britain's June 23 referendum on European Union membership.

BCC director-general John Longworth quit this week after saying he wanted to leave the EU, which the BCC's president said breached the body's neutral position on the EU.

(Reporting by David Milliken; Editing by Angus MacSwan)