The rules on deposits differ slightly depending on whether you paid your deposit before or after 6 April 2007.
If you paid your deposit after 6 April 2007, your landlord should have put it in a tenancy deposit protection scheme.
[Landlord or letting agent address]
Re: Deposits for [your address]
We vacated the above property on [date] and, as requested, returned all sets of keys to [you/ your letting agent] on the same day.
We have fulfilled all of the contractual obligations set out in our tenancy agreement.
We have paid all bills up to date and no damage has been caused to the property.
We were told we would receive a cheque for our deposit from you but this has not arrived.
If we do not hear from you within five working days we shall assume that you are withholding our deposit unfairly and will therefore be applying to the tenancy deposit protection service that safeguards my deposit and request an adjudication and final settlement.