Thank you noworriesmate (love your profile name and pic btw) & Lady Rainicorn.
The matter is urgent, they have been living with rotting walls, kitchen cabinets and a very big damp problem in the bathroom for a while (not to our knowledge, we were told everything was been sorted out.) Anyway there was a leak in a pipe that has now been sourced and fixed, so no more leaking water, but the damage is serious and the house needs weeks to dry out even with dehumidifiers now in place. Also because work is in the bathroom they have to be housed elsewhere while the work is carried out. We don't want to give them notice we don't think that would be fair, and also we need the house fixed asap.
noworriesmate, you said "If the lease is in it's first 6 months then the landlord would be responsible for the costs of re-housing the tenants while the repairs were completed." We are way past the first 6 months, they have been in the house for almost 19 months, do they then have to find their own alternate accommodation?