In reply to joseph_dyball:
If you bought the jacket from a retailer (the seller), then your contract is with the seller, not the manufacturer. I had a similar experience recently and the seller was adamant I had to return the item and they would return it to the manufacturer for investigation. As the manufacturer was in the US, this could have taken many months.
I informed the seller that my contract is with them and not the manufacturer and I was happy to send them the item to identify the fault and to either replace or provide a refund. The seller continued to insist the item had to be sent to the manufacturer in the USA. I offered them the opportunity again to replace the faulty item or provide a refund or else I would take them to the small claims court. The seller provided a refund.
Your contract for the jacket is with the seller, not the manufacturer. It is reasonable to provide the seller with the opportunity to inspect the item. But, if it is faulty, the seller has to repair the item, provide a replacement or a refund. Sometimes a repair is not feasible due to the nature of the item, such as a faulty rope.
There is a very good set of template letters by Citizens Advice here: https://www.citizensadvice.org.uk/consumer/template-letters/letters/
I hope you get this sorted.
CB.