It's very difficult to take it outside. One thing is - show the quotation from outside and tell that you are getting it cheaper there. So you don't want to take it from them. Sometimes they will either agree or they will reduce the premium and match with what you showed.
Another thing is - take from them, and next year onwards, do the thirdparty renewal outside. (thirdparty you need to renew every year, Only standalone will be long term - 3 or 5 years.)