Additional Voluntary Contribution.
Basically, many occupational schemes will require a certain level of employee contribution in order to qualify for an employer contribution. In your case, you had been contributing 6% and getting an employer contribution of 5%. The max AVC by an employee for your age group is 20% of total salary/bonus/other emoluments up to 115k, so that would be 23k if you earn over 115k.
I don’t understand where the 1% you mentioned above comes from, sorry.