ISH has a block Student Possessions Insurance, which covers your belongings inside the building. You can read the details and access the documents online at: https://www.cover4insurance.com/insurance-products/block-halls/international-student-house
Please take time to read this through so that you are aware of what is covered and what is not covered by this policy. It is possible for you to purchase additional insurance, eg to cover specific high-value items you may own, or for added cover when outside of the accommodation (eg a bicycle, your mobile phone or laptop when walking around London). This can be arranged online, directly with the insurers.