Squiggs
TS Team
Depending on what you mean by the 'concept of Towers 2', a 2 Day ticket for Alton Towers was introduced as early as 1984.The concept of "Towers 2" was certainly introduced in the 1990s, which was the ability to spend an additional £5/£10 or so (when in the park) to come back the next day.
It was rebranded to Towers Two in 1993. I'm not 100% sure, but it looks like the old two-day ticket had been discontinued after 1990, in which case Towers Two would have been a relaunch of sorts.