If the average person is twice as rich as they were 10 years ago, I am willing to bet that a majority of the poor are significantly richer as well. Especially consider we all know (given how much politicians talk about it) that income equality was much better during the 80s then it is today. I can't find the stat for Britain, but for America in 1991 the 1% had 13% of the after tax income in the country, compared to the 24% today. Assuming Britain is more equitable then America (because it probably is), then for GDP to double, a majority of that wealth gain would have to come from the middle and lower classes.
Anti-thatchers first claim that she made the country poorer, when the actually statistics are thrown at them, they say she was bad for the poor, again when the statistics are given to them they talk about civil unrest and breaking society. Unfortunately there are no statistics that measure the merit of that argument.
All I can say to that though, was if she was as unpopular as people make her out to be, she probably would have lost an election, rather then won 4 straight majorities governments.