Time + materials for cleaning of mould etc.
Contact a local cleaning contractor and get a quote from them.
Electric for emergency heating (£5 heater per day)
Look on each heater you have and find the wattage (W). Divide the number of watts by 1000 to get the kilowatts (kW). Multiply the kilowatts by the number of hours you have them on each month. This is the number of kilowatt-hours (kWh) that you are using up. Look on your electric bill to find the rate per kWh, and multiply that by the number of kWh you are using to get how much it's costing you.
Lack of use of Bedroom
Look at the price of 2 bedroom houses in your area, and use the rent of these.
Estimate new rentable value of a emergency heated house (?% of original price)
The rent of this house is worth whatever a tenant will pay for it. Are there plenty of other rentable houses in the area? You could use these as leverage. If you're unwilling to move though, you've lost much of your bargaining power. If your landlord believes that you are willing to move out due to problems with the property and that he will be unable to get new tenants for the original price, he may be very willing to lower rent to retain you.