Yes, Polka formula is used by most mothers in the UK - eventually. Just as most of the learner dancers in my ballroom course go on to do do other forms of dancing - eventually.
The majority of women who plan to breastfeed are not using formula in the early weeks of their baby's life - you'd be demonstrating, in a large group, important practical skills upon which their baby's health depends, weeks and most likely months before they need them.
It is far safer for someone using formula for the first time to read the instructions on the tin - don't expect someone (possibly in a crisis, as has been suggested, at 3 am) to remember accurately information they were told months beforehand. (I suppose there my dancing analogy falls down (ha!) because it's not actually a risk to my health if I learn ceilidh steps months in advance :) )
The class is badged clearly as 'breastfeeding session'. No need for anyone to be disappointed, or livid, or outraged, or even surprised, that there is not a great deal of info on formula feeding in it.
All breastfeeding counsellors can offer support and information on formula feeding to individuals, just not in a group setting. If they don't have the exact information (for instance, health/medical related queries about specialist formula; consumer related queries about the best-value bottle) they know where to signpost the mother to get the answers. You talk as if only NCT could possibly supply formula information - and without formula details in the breastfeeding session, parents are left adrift and unable to find other sources.