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One of the principles of a lease is that the tenant has "quite enjoyment" of the space that the lease covers. Having decorators in the house does not constitute quite enjoyment and even less so if you can not even occupy at the same time. LL can not charge you rent if you do not have the benefits that that the lease automatically provides to the tenants. They either cover your additional costs for the time you are out or you don't pay rent.
If it's not done yet, change the locks.
The latest is that they need the tenants to move out for three weeks in order to decorate. The tenants have agreed to do this as long as they don’t have to pay rent for those three weeks, the agents have said that that isn’t an option and they won’t redecorate if the rent isn’t paid.