Sounds like your buyer's solicitor is having an issue trying to update the register at Land Registry.
Once a transaction completes, the buyer's solicitor has to make the usual application to the Land Registry to update the title with the name(s) of the new owner.
Land Registry may have taken quite a while to look at the application (particularly at the current time) and have now raised a query (a requisition) about the application.
It is probably the Land Registry that want the ID1 and won't register the new owners until they have it.
Did this sale involve you selling on behalf of someone else, or was there a discrepancy with your name?
Not an error by the agents, but possibly was missed by your solicitor or the buyer's solicitor during the course of the transaction, or they were not aware that Land Registry would request it. Nevertheless, if you didn't submit an ID1 during the course of transaction, it sounds as though it would have been required.
I don't think you will be able to claim the cost of this - it would be seen as a disbursement, whether it was done 8 months ago or now.