Thank you for your help on this. I've had a closer look at the contract and there is another ambiguity which I'm hoping you might be able to advise on.
The wording of the contract as I wrote before indicates an 'agency period' but in the length of agreement section the agent wrote by hand that it is a 28 day rolling contract. They ticked a box to say the contract was sole agency but in the commission fee section, they do not specify whether their stated fee is for sole or multiple agency. We really want to instruct a new agency without being liable for these fees and wondering whether these technicalities might enable us to end the contract without giving any notice.
In the terms it also says that "the agency shall continue as the sole agency until either
-the seller appoints another agent without giving any or adequate notice in which case the sole agency will continue to apply save that the multiple agency commission fee will be payable if a fee becomes due.