As all.UK Domains are registered with Nominet - The Official Registry for UK Domain Names
They do not allow to deletion of any Glue Records for the Domain.
As if you have added any Glue Record for your domain, you can update them but you can not delete them.
For more information about deletion please contact Nominet and they may help you accordingly
You can contact them by Phone or email.
You need to use the same email you are registered with .UK Domains
You can go to Log In - Nominet UK and Click on Forgotten password? and put your email that you are registered with and they will send you a link through email to reset password, once you have reset your password you can then login and chat with them for the domain support
There is another way to contact them with phone number +44 (0) 1865 332244, +44 (0) 330 236 9480 or email to firstname.lastname@example.org or website https://www.nominet.uk/domain-support/
.ac.uk – academic (tertiary education, further education colleges, research establishments (such as the British Antarctic Survey) and learned societies)
.bl.uk – used solely for the British Library
.co.uk – commercial entities and purposes (the most popular second-level domain for .uk, majority of .uk registrations are on .co.uk domain)
.gov.uk – government (central, devolved and local)
.judiciary.uk – judiciary of England and Wales
.ltd.uk – limited companies
.me.uk – personal names
.mod.uk – armed forces and Ministry of Defence establishments and systems
.net.uk – ISPs and network companies (unlike .net, use is restricted to these users)
.nhs.uk – NHS organisations and trusts
.nic.uk – network use only (reserved exclusively for Nominet UK)
.org.uk – not-for-profit entities
.parliament.uk – Parliament of the United Kingdom and the devolved national parliaments and assemblies
.plc.uk – public limited companies
.police.uk – police forces in the UK and law enforcement organisations.
.rct.uk – used solely for the Royal Collection Trust
.royal.uk – used solely for the royal family website
.sch.uk – local education authorities, schools, primary and secondary education, community education
.ukaea.uk – used solely for the United Kingdom Atomic Energy Authority
.co.uk, .ltd.uk, .me.uk, .net.uk, .nic.uk, .org.uk, .plc.uk and .sch.uk are managed by Nominet UK and except for .nic.uk are available for registration by the public (though they all carry various degrees of restrictions). Other second-level domains are managed by various government agencies, and generally more strongly controlled.
.govt.uk – former government domain, now deleted and replaced by .gov.uk.
.orgn.uk – former non-profit organisations domain, now deleted and replaced by .org.uk.
.lea.uk – local education authorities; since fallen out of use.
.mil.uk – the Ministry of Defence have always used .mod.uk for their external domain, but use .mil.uk on their private network. .mil.uk exists only as a CNAME for .mod.uk in the .uk zone file.
.cym.uk – A second-level domain for Wales; it did not have support of the Welsh Internet community, with a .cym domain being proposed, though later rejected. Top-level domains of .cymru and .wales have since been delegated to the root in 2014.
.scot.uk – A second level domain for Scotland; it was rejected by Nominet. A top-level domain of .scot approved on 10 June 2014 and been delegated to the root since 13 June 2014.
.sco.uk – A second level domain for Scotland.
.soc.uk – proposed for Social and Society use.