My opinion -- sell the 7D, get a 1DII and a 5DII. Would make money on the sale of the 7D+grip for the 1DII. Of course, that would precipitate selling all of your crop lenses, and would give you less reach than the 7D provides.
What are you finding lacking in your current setup? You could move to the 70-200/2.8 IS for ~1100$ (sorry, I don't really work in pounds). As for top wedding choices:
Another flash, off shoe triggers, umbrellas, stands, and other lighting equipment. Sharp lenses are nice, but nothing sets you apart from the competition from a non-photographer's standpoint as creative light and composition.
Sigma 85, Canon 16-35 (or Nikon 14-24), Zeiss 35-70 or Canon 24-70 (I personally hate this lens, but if you move to full-frame there aren't a lot of options), and a 24 or 35 prime would cover you for most shots. The TS-e 45 is pretty popular for engagement shoots.