You have a version mismatch with the version of OpenLayers you are trying to use and the version that is used in https://wikishire.co.uk/map/inset
The JavaScript code used on https://wikishire.co.uk/map/ is Version 6 or above, so looking at the source of your page it seems you need to copy the code from https://wikishire.co.uk/map/slippy.js to replace what you currently have as it uses ‘ol’ rather than ‘OpenLayers’.
