Using a credit card to improve credit rating

Looter

I use my Santander cashback credit card for all my shopping and petrol, I always pay the full balance every month as I understand it helps with my credit rating. I keep meaning to put the amount I spend into a spare savings account so I can simply transfer it when the bill is due, but it's easier said than done! Using a credit card means another bill at the end of the month, which I don't like!

I'm thinking of ditching the credit card, but what I want to know is does it matter how much the balance is when you pay it off in full for credit rating purposes? Is it deemed just as good having a bill for £50 and paying that off in full as having a bill for £300 and paying it off in full?

Thanks for any replies!