Ultimately your landlord has to acknowledge your request and only he/she can agree not to exercise his/her right for compensation for breach of contract.
Reasonable compensation in this circumstance would be to reimburse your landlord for any costs they have spent towards your tenancy term and any costs your landlord would be liable to pay at the natural end of your tenancy again due to early termination/breach of contract.
1) Pro-rata any agency fee paid by your landlord for the tenant find service or any annual fee.
Example if the fee was £1200 (£1000 + VAT) the pro rata monthly figure would be £120, if you would be terminating your tenancy 6 months early you would be liable to pay £720 (Inc VAT).
2) Check-Out fee charged by inventory company.
3) All Utilities, Council Tax and Rent up to the date when a new tenant takes possession of the property.
4) Any difference in rental figure up to and including the end date of your tenancy agreement or break clause. (If a new tenancy cannot be agreed at the same annual rent)
5) Deposit is released as usual subject to satisfactory check-out conditions
6) Standard move out process would still need to be followed.
7) Any miscellaneous cost for things such as relocation of furniture you requested to be moved out and stored for your tenancy term. Specific terms to be confirmed.
8) Deceleration letter to be signed
For a full financial break down of costs please request as these may differ between clients due to the service the landlord has paid for.