What landlords are usually responsible for
GOV.UK guidance says landlords are responsible for repairs to the structure and exterior, sanitary fittings, heating and hot water, gas appliances, electrical wiring, and damage they cause while attempting repairs. Your tenancy agreement may add more detail, but it cannot usually make you responsible for repairs that the landlord must handle by law.
You should still take reasonable care of the property, report problems promptly, and allow access for inspection or repairs when proper notice is given.
How detailed should the repair letter be?
A vague message such as "the bathroom is bad" is easy to miss or misunderstand. A better repair request names the location, describes what has happened, explains the effect, and asks for a response by a date.
If the issue is urgent, say why. For example, no heating in winter, water entering electrics, a broken external lock, or serious mould growth should be treated differently from a loose cupboard handle.
Access and records
Tenants normally need to allow reasonable access for inspections and repairs. GOV.UK says landlords should give at least 24 hours notice and visit at a reasonable time unless it is an emergency. Including access windows in your letter makes it easier for the repair to move forward.