The son of a clothing merchant, Oastler was 31 when he was appointed steward to Thomas Thornhill's estate near Huddersfield in 1820. A less likely candidate for a reforming radical it is hard to imagine - he was a dedicated Tory, against parliamentary reform and trades unions, a paternalist who believed the upper classes had a duty to protect the weak.
Still, he felt strongly about the exploitation of children in factories, and a chance meeting with Bradford worsted manufacturer John Wood in 1830 pointed the way forward. "John Wood turned towards me," he wrote later, "and reaching out his hand in the most impressive manner, pressed my hand in his and said: 'I have had no sleep tonight. I have been reading the Bible and in every page I have read my own condemnation. I cannot allow you to leave me without a pledge that you will use all your influence in trying to remove from our factory system the cruelties which are practised in our mills.'
I promised I would do all I could. I felt that we were each of us in the presence of the Highest and I know that that vow was recorded in heaven."
The same month, Oastler wrote on the subject to the Leeds Mercury. Radical MP John Hobhouse read his letter and was prompted to introduce a child labour bill in the Commons which would have banned all factory work for children under nine, and limited those between nine and 18 to 12 hours a day, 66 hours a week.
Unfortunately, Parliament was dissolved before the bill could be passed, and when it was reintroduced in 1831 Hobhouse had agreed to changes: As passed, the bill applied only to cotton factories and there were no provisions for its enforcement.
Oastler and the short-time committees that were now forming in industrial towns were irate. The man they called the Factory King continued the battle as leader of what was now known as the 10-Hour Movement and by 1836 he was urging workers to use strikes and sabotage. This proved his downfall.
His employer, Thornhill, hearing of his speeches, sacked him as his steward and called in unpaid debts. Oastler was unable to pay up and was jailed for debt in December 1840. It took his friends more than three years to raise the cash and release him from the Fleet Prison.
Oastler went straight back to his campaign and achieved some sort of success when the 1847 Factory Act restricted children to a 10-hour day in cotton mills. But it was not until six years after his death in 1861 that the act was widened to encompass children working in all factories.