This will have no impact on your credit limit directly. You'll be able to increase your spending power without any additional borrowing.
This will not impact how your account is reported to the credit reference agencies.
e.g With a £500 credit limit and £200 on your top-up, this will give you a spending limit of £700. This will continue to be reported as a £500 credit limit and if only £200 is spent on the card the credit limit would be not utilised.