If someone sends an email from Spain using a Hotmail.co.uk address, is it possible for the X-Originating-IP field of the header to show a Uk IP address?
If they're connected through a proxy or VPN, yes they could show a UK IP even if they are in Spain.
You can do an IP Address Lookup to get the location of the IP. Or an IP Whois Lookup to find out who owns the IP. If IP Whois ownership is reported as an ISP, chances are they're in the UK and not Spain. If IP Whois ownership is reported as a VPN service, then there's no telling where they are located.