The CBI says growth reached a record high in May, marking the best reading since it began gathering data in 2003, the BBC reports.
Meanwhile, the BCC upgraded its growth forecast for 2014 from 2.8% to 3.1%, which, if achieved, would be the highest rate since pre-crisis 2007.
That figure is well above the 2.7% forecast by the OBR.
The OBR, or Office for Budget Responsibility, is the government’s independent fiscal watchdog.
The CBI’s growth report suggests the UK economy has continued to perform strongly in the second quarter of this year.
It expects the pace of growth to remain firmly above average for the coming quarter as well.
Stronger economic performance was seen across the board, said the CBI.
Sectors including retail sales and professional and consumer services did well in the three months to May.
Manufacturing output also continued to grow at a similar pace to the previous two months.
Katja Hall, CBI deputy director-general, said the improvement was down to increased confidence in the UK economy, easier access to credit, and better global economic conditions.
However, Hall said there were risks to the UK’s outlook from global developments, including the “possibility that the situation in Ukraine and Russia could impact on global commodity prices”.
She added: “With the eurozone crisis still far from being fully resolved, the UK continues to be exposed to a prolonged period of subdued activity in the region.”
The BCC also said the economic recovery was not guaranteed.
