Apparently Captain Britain #3 doesn't know Cockney slang. We're not going to translate it here, because that would rob you of the fun. Actually, it's just #2 who's using slang - #1 is only written in a bad accent. Nobody actually talks like this, by the way; it's a cartoonish exaggeration.
The Crosstime Caper is a real thing, though: it was a storyline that saw Excalibur, Captain Britain's team, bouncing around the timestream, meeting a lot of other Captains Britain in the process. So seeing multiple Caps in varying costumes, the original assumes he's come unhinged again.
The figures, from left to right, come from the Marvel Universe line, the Captain America movie line, and the International Patriots box set. The two on the right are shorter than the one on the left, so they're standing on a little thing to give them a boost.
The title of the strip is inspired by Stephen Colbert's standard interview question: "George W. Bush: great president, or the greatest president?"