Perhaps you haven't noticed, but an element of this thread has had to do specifically with how far back one needs to look at political matters. When one is in one's late seventies, 50 years ago is but a passing breeze!
The point is that Tories and/or their supporters are forever claiming (a) to be "the party of economic competence" and (b) that they invariably leave a booming economy which Labour goes on to wreck. I'll bet Maudling had "a long-term economic plan that was working", too, only it was no more effective than ANY of the economic promises Osborne made five years ago, all of which have turned to dust. No rise in VAT…Oops! Deficit wiped out by 2015…Oops! I could go on, but I’ll leave it there.
However, if you need something more recent than 1964, how about Black Wednesday? Yet another example of Tory economic incompetence though, obviously, I have no idea whether you are old enough even to remember 1992. They’d been in power for 13 years by then, so no way in the world to blame Labour for any “appalling legacy”.
The details of that day are well known, so I’ll just leave you with a link to a photograph (the top left one) of a shadowy figure lurking in the background as Norman Lamont faces the press. I’ll bet Lamont had “a long-term economic plan that was working”, too, and Cameron was his adviser and speech-writer!
https://www.google.co.uk/search?q=lamont+black+wednesday+picture&ie=utf-8&oe=utf-8&gws_rd=cr&ei=CYNEVY-8L8LgaIOVgYgG
PS You may also not have noticed but the Tories have never done anything about cancelling the Corporation Tax Jim Callaghan introduced, so clearly they thought it was a wonderful idea!