I have been continuing to research this issue and have made slight progress.
From the code in my initial post I have replaced:
let url = getItem.url;
with
let url = wixLocation.to('/class-20-loco-data/${$w("#numberDropDown").value}');
This amendment now sees the url change when I click on one of the dropdown options but unfortunately it changes to https://www.ukraillog.co.uk/class-20-loco-data/${$w(%22 which, rightly, brings up a 404 error message. If I overtype the ‘$%7B$w(%22’ part of the url with a number from the dropdown list, it correctly takes me to the relevant page but then if I click on a dropdown option again it reverts back to the incorrect url.
I feel like this has taken me a step closer to a solution but could do with the expertise of this forum to point me towards the finish line please ![]()
Thanks