Final percentage will not be known until the budget statement. It will be the higher of three factors:
Consumer Price Index (CPI)
Wage growth
2.5%
Wage growth is currently winning at 8.5%. The govt are reneging on the Triple Lock gaurantee and considering stripping out bonuses from annual wage growth figures. That would bring the rate down to approx 7.8%
In a nutshell; pensions will increase in line with wage growth of either 7.8% or 8.5% depending on bonuses in or out of the calculations.
Gentlemen, start your calculators.