If you are a member of the Professional Contractors Group (and I'd recommend it if you are not) they may be able to help.
Without seeing the terms of the contract, you may be a 'nominated resource' of your limited company, and it is the company that holds the contract - so the company could be sued. You could provide another resource (possibly by subcontracting, or taking on an employee for the duration of the contract) but much depends on the wording of the contract.
But get professional advice.