There are two versions of the electoral roll. The version which 192.com purchases only includes people who've not ticked the box which gets them removed from the edited version (which is also sold to advertising companies to produce mailing lists).
Since the vast majority of people now tick that box (to try to reduce the amount of junk mail they get), 192.com's database actually only has a fairly small percentage of registered voters on it.
So, even if you use 192.com, your chances of finding a particular person aren't necessarily that great. To the best of my knowledge though, 192.com is the only company that purchases the rights to used the edited roll as a publicly-available database, so it's 192.com or nothing. Sorry!
The full version of the electoral roll (with all registered voters on it) isn't available in electronic form to the general public. (Only the police, security services and credit reference agencies have access to it). Local authorities have to make the print version for inspection (so that people can check that they're registered to vote) but they now seem to be tightening up the rules about viewing it.
For example, here's what appears on my local council's website:
"The full version of the register contains the details of every registered elector. Access to this register is restricted by law and the use of the data is limited to certain purposes.
A paper copy of this version is held in by the Electoral Services Team at the Council offices. This may be inspected, under supervision by a council officer, by any person during usual office hours (subject to satisfying the Electoral Registration Officer as to the necessity of seeing the full information rather than using the open version of the register). You must make an appointment to view this register in order to ensure that there is someone available to supervise your viewing. Please contact Electoral Services to make an appointment.
Handwritten notes are not permitted. The use of copying machines, photography and computers is not permitted. This includes entering data into a mobile phone or electronic device.
There are restrictions on what information obtained from the full register can be used for. You will be required to complete and sign a declaration form prior to viewing"
Further, even if you can get to see the full electoral roll, it's not easy to find a specific person. The information is listed in alphabetical street order and not cross-referenced alphabetically by people's names.