How to obtain an NIC for dual Citizen?

I've been a Dual SL citizen since 2017 but through ignorance never obtained an NIC. Now that my SL passport needs renewing, I'm required to have an NIC which I cannot obtain in the UK.

Can a family member apply for an NIC on my behalf in Sri Lanka? Failing in which I could go to SL and get it done.

If I travel to Sri Lanka, I understand that there is a 1 day service to obtain the NIC, however I don't know if the Grama Niladhari / Divisional Secretariat attestation of the application can be done on the same day?

My original thinking is that I could spend a week in SL sorting all this out, doing the one day NIC and one day Passport renewal services, but I'm having doubts as to whether it is possible.

Any advice is appreciated.

If only all application processes were digitised as they are in the UK!