Yes, this is achievable and quite simple to do so. Go to Settings > Permalinks in your admin area.
There you should be able to select Custom and use a value like (if you want all URLs to start with /carhire/uk/)
If your logic is more complex, I suggest using a plugin such as Custom Permalinks.
I just tried it myself, on the wordpress.com free plan it seems that you can't change permalinks at all (neither via settings nor via plugin). If you upgrade to the Business plan (~24$/mo), it is possible to install plugins - and the aforementioned should solve this.