Minimum payment varies between credit card companies. The lower the minimum payment, the longer it takes to pay off and the more interest you pay - assuming you only pay the minimum payment each month.
It can be between 2 and 5% of the outstanding balance. The minimum payment does not always cover that month's interest, so you pay interest on interest and the debt grows.
As you have seen, it is complicated and there is no one simple answer.
In your example, interest in the first month would be �14.59. Assuming minimum payment of 3% - �30 - roughly half of the payment would be interest and the remainder off the principal.
In month two, the outstanding balance would be �985, so the minimum payment would be �29.55, and the interest payable �14.36.
The formula for calculating the monthly interest is:
Balance x APR% / 12
This is a simplified estimate, but is not far out at all.