What to do when PI is not obtainable

What options are open to the contractor when they can no longer obtain professional indemnity insurance at commercial rates for the indemnity level stated in the Contract during the Rectification Period [defect period] and there are still defects to clear during the rectification period, but the Employer refuses access to the site until the Contractor proves that it has PI cover in place in accordance with the level of indemnity stated in the Contract?