My CFO wants to an approval workflow in place for Bank Details, so if a user edits the bank details of a Vendor this needs to be approved by the FD. Anyone know if this is possible/have any suggestions on how to acheive?

Not easily. But, you could either have a workflow run on a trigger that if a change is made then an approval would be sent out, however, this requires the change to have already taken place which is sort of cart before the horse... Alternatively, you could lock the bank details except for a field called new bank details. The users can then enter that info into that field which would be routed to the approval queue and after the approval that data be translated to the correct destination and the editable field be cleared.

@swojnicz some other suggestions are to set the credit limit to 0 or inactivate the vendor while the approvals are pending. But I like @Camden (WMP)'s suggestion of alternate fields if you're trying to continue doing business with the old details while approval is pending.

Thanks for the suggestions