Sadly, there's only a couple of British publishers and they generally won't accept ideas unless they're written up as full scripts and obey their various submissions guide lines. 2000ad for example, when it does accept unsolicited submissions, requires them to be in the form of 4 page future shocks.
There are a few small press comic publishers who are more flexible, but even those often get so many scripts that it's better to have an artist attached.
Finding an artist can be tough, many writers tend to find them among their own friends or circle of friends. Sometimes it's easier to draw your own work - it doesn't have to be great, just good enough, and put the stories online and bring them to comic shows to sell. That's how Al Ewing began his career and he's now working for marvel.