As the clients are the accountants and not yours you would not need to do an MLR as the accountant has done this. it will probably be stated in any form the accountant asks you to sign. The document will usually also state that everything is confidential, you can't poach clients etc.
If you were being paid by the accountant you would need to do an MLR on him/her. If at this stage he does offer to pay you I would suggest you ask to be paid by PAYE even if its a zero hour contract.