When forming a model boat club I had the greatest uphill battle with councils, even just getting them to allow electric boats to sail, the slightest mention of I/C and they flatly refused.
if its a river you use, or thinking of using, then speak to CRT [Canals & Rivers trust] formerly British waterways, they are quite helpful in situations like these, but don't be shocked if issues arise from I/c AND anglers, as the anglers pay a licence fee to fish those areas and they wont be too happy with someone either "scareing" the fish or cutting lines [ha ha]. We as a club found some great water sailing areas, but angles had already got pitches there and we were refused without any further consideration.
You will also need to get some 3rd party liability insurance cover, as sailing in a public place and all that..........
YES, have a search around see if there are any local model boat clubs near to you, as they will of already got all the above sorted and got specific sailing areas, all with full permission, so you wont have to do the groundwork.