When should I effect building and life insurance when purchasing a property?

The normal rule is that risk in the property passes upon exchange of contracts (referred to above).Therefore upon exchange you have an insurable interest and that’s when building insurance for the property’s full reinstatement value must be taken out not on completion.
Similarly any new or existing life insurance which needs to be increased should also be placed on risk at exchange not completion because in the event of any purchaser dying their estate will still be liable to complete the purchase but the estate would not have the funds to purchase the property.