Want to disallow users from changing 'manual proxy ' setting from windows settings

My experience is that once the GPO sets proxy, it does not unset it.
If you want to push on a per user basis on specific systems, use GPO with loopback processing assigned to the computer OU add the user settings for proxy, this way the proxy will apply on login rather then be committed to the user's registry ....
Part of the settings could be to disallow user changes/visibility.
The other is on the external firewall block outgoing port 80 requests from all sources except authorized IPs, systems and the proxy servers.

Depending on your firewall such Cisco where you can implement a transparent proxy wccp that will reroute based on ACL outgoing port 80 requests through one, several proxie cache system... The difference, if wccp fails to establish connection to an available proxy the user's access will not be impacted as the ACL rule will be negated allowing the user direct access to the outside until the wccp connection is reestablished.

@Masnrock: I tried this on my local machine's gpedit.msc for now (Windows 10 pro), but its not working..

@arnold: you are right and thats my requirement (I dont want to change the proxy setting latter, instead want to leave them in place). For now I just want to disallow users from changing proxy setting using windows proxy setting page..

I have set the connection tab hidden but some of the users are using this back door to play with proxy setting.. :)

Thanks

Another option is to use wpad, DNS, DHCP based proxy advertising with the GPO you lock out the user while at the same time set auto proxy detection.

Guys, it will be great if you can help me with what I am looking for..

What do you mean? https://technet.microsoft.com/en-us/library/cc995261.aspx

@Arnold, I just want to disable the 'use a proxy server' button under 'manual proxy setup' as highlighted in very first screenshot..

Its not helping at all. If you will check, this KB is applicable to windows 7 and I am on Windows 10.

Any one can just help with one key value or GPO setting for this particular option that I am requesting for?

Thanks

Proxy settings apply to ?I?e11, the guide covers the implications.
It can be used by reference to facilitate what you want to achieve.
Try it on one system using security fikter to apply this GPO to a single test system. Then if it works, app,y it to others. If it does not look at whether the issue that the settings are not seen by the ad DC server version. Install rsat and gpmc on your Windows 10 system and see whether the options you wish to set are now visible within GPO or group policy preferences.

Guys, the very first solution worked well. Not sure, why it was not working earlier (possibly I was making some mistakes).

problem resolved.. thanks guys..