So how come if the UK is the 5th largest economy in the world have so many people been left disenfranchised / left behind/ struggled with infrastructure issues ?
The quick answer to that is that many other Countries have much bigger problems than UK. I have been fortunate enough to work in over 20 Countries outside UK and seen first hand.
Whilst UK is 5th largest, there is still a big divide between North and South and the have and have nots.
USA, China, India and Japan will always have stronger economies than UK due to their vast populations. So at best UK could only be 5th in the World
We have achieved that status whilst benefitting from being a member of the EU, are you suggesting the UK will climb up to 3rd or 4th place once out of the EU ?
In 1960 UK was 4th largest Economy behind; USA, Soviet Union and West Germany.
In 1965 UK was 5th largest Economy behind; USA, Soviet Union, West Germany and France.
In 1975 UK was 6th largest Economy behind; USA, Soviet Union, Japan, West Germany, and France. Japan by getting themselves organized pushed both Germany and France down the list.
Between 1975 and 2015 UK has fluctuated between 4th,5th and 6th position. Take 5th as average and that is lower than the 4th position in 1960, 15 years before UK became an EU member.
Dilution is the explanation. As the EU expanded an accepted Countries who were nowhere near as developed the stronger Countries ended up subsidizing them at thei cost.