From an insurance point of view, the policy hasn't been renewed. The policy is renewed on the renewal date.
Your contract with the insurance company for the policy which renews on 31st July commences on 31st July - so you are not cancelling the policy, you are deciding not to renew the policy.
It matters not a jot that you have verbally agreed to renew the policy.
As you are not cancelling the policy, you cannot be charged by the insurance company.
To discover whether Swinton, as the broker, can charge you for work already done will be determined by the Terms of Business Agreement they will have provided you with - but I doubt they can.