You know what? No assumed annual price rises. According to my bills the prices remained stable for 5 or 6 years at a tine. Then, with the advent of the "free market" came the first tentative 0.5% or 1% rises.
Now it seems to be "Bung another 15% or 20% on, nobody in authority cares - nobody can stop us"
I think that perhaps, (in some ways), we had it good back then, in as much as corporate industry had at least some concern for their customers and at least had the good grace to blush and apologise about the very occasional 1% rise in prices.
I'd have said "rose coloured glasses", except that my old energy bills seem to suggest not.