I would write back and say that I was very unhappy with the bill and that he had gone beyond my instructions and/or the fees do not reflect what has actually been done. I'd then state what I was prepared to pay (a reasonable amount) and state that if that was not acceptable, I would like a copy of the WIP report (WIP=work in progress) and a full breakdown of what items have been charged and why and exactly what those consist of; as well as details of what has not been charged and why. He might take the view that by the time he's spent several hours doing all that, he may as well just have accepted your offer, written some of the bill off and got on with the next job.
I'd think about changing your solicitor. If you are getting divorced, you can do without this.
1. Were you given a fixed quote? 2. Were you given an approximate estimate and how much? 3. Did their terms of engagement say anything about fees and estimates? 4. Could you roughly tell us here what they did and how many hours at what hourly rate they put down for it?