For the 12-month period to May 2014, Conference Care saw the average net spend per event increase, while it also found that day delegate rates rose in London and Manchester.
Day delegate rates in the capital in May 2014 were £59.40 compared to £56.35 in 2013, showing an increase of more than 5%.
Manchester showed an increase of 6.5% with day delegate rates at £37.80 last month compared to £35.50 the previous year.
However, day delegate rates in Birmingham averaged at £40 per person, showing no significant increase.
Louise Lowe, sales director at Conference Care, said: "Confidence in the economy is gathering momentum. The number of confirmed events that took place in May 2014 is up by 15% on the same period last year.
"With the upturn in both events’ value and volume, the forecast is looking good."