Shipping luggage back to UK while on holiday (UK resident)

Hello, I'm a UK resident and travel a lot. I'm planning to go to Japan for one week (approx. --15 degrees celsius), and then backpack through Thailand/Cambodia (30+ degrees celsius) for 2 weeks. For Japan, I'll have a suitcase filled with winter apparel/gear (parka, snowshoes, boots, etc.). Instead of lugging this around while I backpack through SE Asia in 30-degree heat, I'm considering shipping this suitcase back home, and then arriving 2 weeks later. [1] Could you please tell me if I will owe any money to the HMRC? To be clear, the suitcase will be filled with my own used personal belongings, ALL of which I had purchased in London. [2] For the purposes of HMRC, what form will I have to fill out and how should I declare my goods? That is, what should I actually write? [3] Does any of this depend on the goods' value? (there's a £1k-parka, if that makes a difference, but it's otherwise of reasonable value). I have never dealt with customs before and would appreciate a simple explanation. Thank you in advance :)

Hi Fabian,
If customer is sending personal belongings back in a shipment, the shipping company should handle all the customs formalities.
Customer can look in to claiming returned goods relief, ask the sender to write:
Returned goods — relief claimed’ clearly on the package and its accompanying import declaration.
The declaration must include a complete and accurate description of the goods, their quantity and value.
More information on below link.
How to claim
Thank you.