Unfortunately, you can only end a fixed term tenancy early if you either use a break clause in your contract if there is one or negotiate a surrender with your landlord.
If not you remain responsible for the rent until March 2023 unless you can find an alternative acceptable replacement tenant.
As to the issue of the Gas Safety Certificate, failure to comply with the Gas Safety Regulations is a serious offence.
Being unable to provide a gas safety record is a criminal offence and landlords can be liable for unlimited fines and/or six months of imprisonment.
This is also classed as a hazardous situation and landlords can be subject to enforcement actions, such as prohibition or improvement notices or even emergency remedial action by the local authority.
Under the Deregulation Act 2015, all landlords of assured shorthold tenancies on properties where there is gas, must provide their tenants with a valid gas safety record before the tenancy begins and failure to do so means the landlord is unable to serve a Section 21 notice.
If your landlord refuses to provide you with this, you should contact your local authority and let them know.
You can certainly use this as a bargaining ;to get the landlord to agree to a surrender of the tenancy but it is not necessarily a breach of contract unless you argue it interferes with your peaceful enjoyment of the property and puts you at risk.