Tried to search a domain name using first reliable site: the domain name I was checking was not taken and available as both. Com and. co.uk versions. Then tried 123-reg.co.uk and the same domain name was apparantly taken and not available. Went back to reliable site and the names that had previously been not taken and available were suddenly (in an interval of one minute) taken and not availble in both. Com and. co.uk versions!
I can not prove it but it appears as if 123-reg.co.uk was just capturing any domain name you search for so that you would have to buy it!