The decline of industry since the 70/s is well documented, as are the causes. Were this a feature unique to Britain it would be a major cause of concern. HOWEVER it is a decline shared by all advanced western economies. It is a fact of life. Meanwhile other fields of employment have been created. It is a reality, and is an ever changing dynamic. It started long before the common market was ever dreamed of. Industrialisation created both better agricultural machinery and lead to a dramatic decline in agricultural workers. In 1800 30+% of the labour force worked in agriculture, today it is roughly 1% with a consistent decline up until about 1980 when it slowed. Coal mining peaked in 1920 employing 1,191,000. By 2015 the number was 2000.
In 1971 the steel industry employed 350,000, 32000 today.
Constantly bringing up the decline of industry in a discussion about brexit is merely a red herring. It contributes nothing to the debate. It is pointless. You would be better off considering the impact of technology in the future rather than harping on about a mythical golden age that never existed.
You cannot cherry pick progress, it comes as a package.