The 6-year rule

Having read through a lot of posts on here, I am just after some clarification on the 6-year statute barred rule.

Is it from the "cause of action" (i.e. a default date), or does it start when the last payment is made towards the debt / or acknowledged it ?



Solicitors/claimants would obviously side towards the latter, but I have seen quoted on here the former, and has this ever been tested successfully ?



Thanks

The 6-year rule