Land Registry fees- no, its not ( entirely)set in stone , particularly if this is a new build -Land Registry assess at time of lodging dealing.
When does the stamp duty get paid? Does it have to be immediate?
Stamp duty is due by you to Revenue within 30 days of the Deed. BUT if you are getting a mortgage, it is a condition of the Solicitor releasing the Mortgage Cheque to your Vendor that he is in funds for all outlays. In advance.
If I have a cash client, I advise them on their Stamp Duty obligations, confirm that I cannot register the transaction without the Deed being stamped and advise that penalties and interest will arise in due course.
If you paid a deposit on a purchase then your solicitor is not holding it - your vendor's solicitor is and it is nothing to do with you or your own solicitor. However, if you are selling and someone has paid a deposit to your solicitor which has earned or could have earned interest, then yes, your own solicitor should account to you for it.
mf