Yes, there is IELTS, as explained in the posts above.
What I was saying, if the dependents do not get 4.5 overall (dependents have been explained above by MaggieMay), you have to pay the 2nd Instalment, aka VAC2, aka English Education Charge (EEC).
This fee is in theory for taking English classes, but this is not compulsory, nor should you pass any test afterwards.