Are you sure all of those are redirecting to .co.uk? I ask this because a person or script analyzing .UK domains may well have forgotten not to include the websites that are forcing redirects to the WWW subdomain. 13% seems pretty high to me.
The top 10 matched (same domain name stub in other TLDs) redirects 8.89% are:
.co.uk 167,249 (7.94%)
.com 12,869
.org.uk 3,977
.org 546
.net 505
.eu 382
.me.uk 320
.de 277
.co 207
.nl 176
The external TLD redirects which don't match the domain names in other TLDs: 19,388 (0.93%)
The internal (same site) redirects are at 0.84%
The HTTPS redirects (the site redirects to the HTTPS version) are at 1.54%.
The same zone redirects are at 1.12%
Unclassified redirects are at 0.36%.
The .CO.UK subdomain is the most used subdomain in the ccTLD. This pattern of brand protection redirects is exactly what would be expected with a newly launched TLD or subdomain targeting the same market.
Most of the names in question are not "brands" but simply keywords, and it's unlikely someone with webserver.co.uk is also going to need to spend a premium on webserver.uk, since Webserver is not a company name.
The .UK domain names are quite diverse and though there are generic domain names in the set, many are not generic. This is a survey of all 2,105,428 .UK domain names and their websites. There were 3,605,478 .UK domain names registered but 1,500,050 were not in the zonefile as they had no nameservers.
I would be interested to see examples of businesses that redirect their .uk domains to .co.uk.
That would require surveying the non .UK domain names and their websites. That's approximately 9.24 million domain names.
Regards...jmcc