Well, there’s a bit of a problem: Thatcher came to power in 1979, and imposed a radical change in policy almost immediately. But the big improvement in British performance doesn’t really show in the data until the mid-1990s. Does she get credit for a reward so long delayed?
This is, by the way, somewhat like a similar issue in America: right-wingers were eager to give Ronald Reagan credit for the productivity boom of the Clinton years, which also didn’t start until around 1995; if Reagan could get credit for events that were 14 years or more after his 1981 tax cut, shouldn’t Richard Nixon be given credit for anything good that happened in the Reagan years?
Anyway, I guess there is a case that the Thatcher changes in taxes, labor regulation, etc. created a more flexible economy, which made the good years under Blair possible. But it’s an awfully long lag.