If you went out on your own could you do more than the £185 per day?
That’s an indicator that your staff might be not working as hard as they should. If you can go out and comfortably do £300 on your own, then they are definitely slacking.
On the other hand, if you go out and do a full long hard slog of a day for £250, then £185 for an employee is not far off.
An employee is never going to put the effort in that the owner would.
At £10-£12 for a three bed semi, surely they could do 3 of those in an hour? It sounds like they are doing far less than that.
Is your work compact or spread out too, that has a big impact.