Update: Version 2.0 released on 9th June 2021, on the WordPress plugin repository.
This, my third WordPress plugin (and also my third WooCommerce plugin, apparently I really like doing stuff with WooCommerce!) adds a postcode lookup tool to the checkout in WooCommerce 3.x that lets your UK-based customers quickly fill in their billing/shipping addresses based on their postcode.
It utilises the great getAddress.io API for the postcode lookup, and as such requires an API key for their service. I’d always recommend the £10 per month pricing plan, simply because it offers the best value, but they have a number of others available.