as the above all say no you do not need to provide one as your are not their employee.
If you are running your own limited then they could state that the support provided by your limited company during the past week was not acceptable and may constitute a breach of contract as your co failed to provide a suitable replacement (assuming you have an ROS clause in the contract).
Your co may then need to provide evidence that their employee (e.g. you) was actually ill (in the form of a doctors note) and also that your co made a resonable attempt to source a suitable replacement. The client may also look for documetation or evidence of the communications which passed between your co and them keep them informed of the situation and a likely end date to your co's inabaility to provide support/service at the levels agreed in the contract.
Realistically I imagine the client co are looking for reassurances that you were genuinely ill and not simply having a bit of a jolly.
If you are running your own limited then they could state that the support provided by your limited company during the past week was not acceptable and may constitute a breach of contract as your co failed to provide a suitable replacement (assuming you have an ROS clause in the contract).
Your co may then need to provide evidence that their employee (e.g. you) was actually ill (in the form of a doctors note) and also that your co made a resonable attempt to source a suitable replacement. The client may also look for documetation or evidence of the communications which passed between your co and them keep them informed of the situation and a likely end date to your co's inabaility to provide support/service at the levels agreed in the contract.
Realistically I imagine the client co are looking for reassurances that you were genuinely ill and not simply having a bit of a jolly.

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