I have upgraded from Internet Explorer 7 to 9, and now I cannot connect to some of my favourite websites or my CCTV cameras through my home hub.
Is it possible for me to downgrade back to IE7?
This could be a rare issue that some of sites are not working with new and better IE, and likely due to other factors like cache having old site data, and also same with cookies, first thing to do before you downgrade back to IE7, I suggest you to troubleshoot what's wrong with sites that aren't working with IE9.
First, Clean-up site data, cookies and cache.
Settings>Internet Options>From General Tab>Click delete from Browsing History section.
and mark everything and click delete.
Now, restart the browser and see if the sites that didn't worked previously are working now.
Regarding the access to CCTV cameras via home hub, the web app you're using might be designed specifically for IE7, though not likely.
Also, try visiting the sites from "In Private mode" as in this mode, IE will not use cache or site preferences stored in your computer, and thus, will request new site data, that might solve the issue.
And still this doesn't solve your problem, you may visit this site for the method to downgrading to older IE.
I have downgraded to ie8 from ie9 once due to a different problem.
How to do it:
Uninstall the ie9 update.
Control Panel -> Uninstall Program -> View Installed Updates -> Internet Explorer 9 . Uninstall it.
this Techdows page. You will find how to downgrade to ie8. Same way for ie7 too.