There is a way of inputting your established use of the helipad into the planning process, I believe. There was a long established helicopter maintenance outfit, based on the edge of an industrial estate, with rural areas to allow approaches /departures. A developer wanted to put a major development on the approach and departure routes. It took a long time and much effort, but in the end the developer had to build them a new building and helipad on a new nearby site, in order to be allowed to develop the area he wanted to.
If you PM me, I can provide details of the maintenance company. They are very helpful and I am sure would be happy to provide information and the name of their consultant.
It won't be cheap though........