What is the ruling on paying a monthly insurance premium to an insurance company to rent an apartment in Britain after paying an initial deposit, if non-payment will lead to losing the apartment and the amount paid?

If you are compelled to participate in commercial insurance to avoid financial loss, there is no sin upon you in doing so, as long as you were ignorant of its ruling beforehand. This is considered a case of necessity. However, you are not permitted to benefit from the insurance more than what you have paid. If you receive anything in excess of that, you should donate it to the poor and the needy. If it is possible for you to negotiate with the property owner for him to undertake the insurance in exchange for an increase in rent, then do so to avoid entering into a forbidden contract.