This is a Nominet accounting status code indicating the registration status of your domain name. Even though it says “Registration request being processed.”, this also means your domain is fully registered. Once 30 days has passed, the status will change to “Registered until renewal date”.
Nominet explain the (sometimes confusing) status as follows: “This status is used after first registration but before the initial registration fee has been received. Please note that we (Nominet) issue monthly invoices, so it is possible that if this status is displayed your registrar has not yet been invoiced for the domain name.”.
For more information, see Registration request being processed at Nominet.