"Set Square" wrote

Other than the fact that this does not conform to current regs (but
won't be visibly flouting the rules) -

Which regs do you have in mind?

I may have been wrong in mentioning regulations applicable to existing
installations.
But, toilet manufacturers are now using Defra guidelines to design cistern
capacities and assess flushing performance.
As most users of the new offerings are finding, these recommendations lead
to woefully inadequate flushing and, just as importantly for people with
inquisitive children, bowl cleaning.

Phil