Tenant staying on due to self-isolation

Other

The tenancy for a 5 bedroom student house was due to end on 10/07/2021. On 09/07/2021 I received a call from one of the tenant saying they had tested positive on a lateral flow test and would need to isolate, pending a positive PCR, until 18/07/2021. They told me they wanted to stay in the property and I said on the phone that was fine and I would pay the utilities (as they had already closed their accounts). I then emailed the tenant to discuss the rent for the week, as I was going to offer a reduction due to it being a large 5 person house, and they have replied saying they do not believe they should pay rent as it is beyond their control and they did not want to endanger their loved ones at home. They are essentially saying they had no choice. When we spoke on the phone we did not explicitly agree rent however I took it to be implied as he was just basically asking for an extension of the tenancy in my mind to cover the period. He is refusing to pay, can I deduct the rent worked out per day from the deposit?