I would like to become a ballroom/latin dance teacher in the UK, and in due time, start my own business offering classes and private tuition to adult social dancers.

I am middle-aged, with experience of teaching/coaching adults but not in dance, and a reasonably proficient social dancer with many years experience.

I do have the Professional Syllabus of the IDTA, and can see what is recuired to obtain, say, the Associate qualification in Ballroom or Latin, but don't really have much of an understanding of the practical route that a keen and committed amateur social dancer takes to become a teacher. My existing teachers are nearing retirement, and have said that they couldn't consider taking on a student teacher in theri own business, and I don't have any other established relationship with other teachers.

Could anyone familiar with the UK scene take a minute or two to give me some pointers, or suggestions as to how I might best proceed?

"My existing teachers are nearing retirement, and have said that they couldn't consider taking on a student teacher in theri own business, and I don't have any other established relationship with other teachers."

Then you will need to find additional teachers and build a relationship with them. Not for the employment prospect, but to provide and continue your training itself through to the professional level. You need to be out and about, plugged into the dance world, not having your horizons confined to a single studio. Think about it this way - even if your current teachers offered you a job, unless you have a wider awareness that would be your only job option!