This article will explain how you can verify your domain name with Google's webmaster tools using your DNS.
Google Webmasters Control panel
Click on the Add a site... button.
Type in the Domain name and click on the Continue button.
Select Alternative methods from the Verify ownership section and then choose Domain name provider.
Select 123Reg from the drop down list to display the verification code.
123-reg Control panel
In the Domain names section, select the relevant domain name in the drop-down list and click on the Manage button.
Click on the Manage DNS option.
Scroll down to the Advanced Domain Settings section and click on the Manage DNS (A, MX, CNAME, TXT) link.
From the Advanced DNS tab.
Select TXT/SPF from the Type drop down list in the Add new entry section.
In the Hostname field enter @.
In the Destination TXT/SPF field enter the record you have been provided with by Google.
For example: google-site-verification=uwvZ73hy7s0aScEc60SkGOukywfzupXroS8hy6itXno
Click on the Add new entry button to save the new record.