It isn't difficult, but it certainly won't be quick. You currently have around 600 items for sale, not to mention numerous recent sales. You won't be able to close your account until all fees etc. are paid, or within the period in which any of your buyers could use eBay's money back guarantee. Think in terms of months, not weeks.
For full information, go to https://www.ebay.co.uk/help/home and enter "close" or "close account" in the search field.
