There's nothing wrong with factory jobs, or any other jobs.
However, at some point there will just be no need for them in the economy. Most factory job that the average 75-85 IQ person will be doing can be automated away within the next couple of decades. A lot of them are already automated.
UK will never be a factory job powerhouse, employing a ton of people in factories. The time for that has passed, and even if we bring back factories and production into the country, it will be automated factories requiring very few actual factory workers.
Heinz is the newest example, who just pledged to invest into a UK production line for their sauces. They are going to produce their entire UK sales here in the UK, investing $200 million into their product line, but are only planning to employ 50 people permanently. 20 years ago the same production capacity required almost 1000 full-time workers.
https://news.sky.com/story/heinz-brings-ketchup-manufacturing-back-to-uk-in-140m-investment-12321966