I used to be with City Index but decided to move to CMC and havent looked back.
I left for that exact reason, I found it went down quite often, particularly annoying when I was wanting to trade at the time.
I've found them to be much better to be honest. I did like CI, but definitely glad I made the move.
Only downside is you can't use a downloadable platform with CMC, although their online platform is great.
edit: just seen you've been with them forever, so guess you're not interested in switching. If thats the way you feel then fair enough, I understand loyalty. Still though there are brokers out there than can offer better services. Down to you I guess