Julian, I use GKFX.
I was going to open an account with Alpari also but at the moment cannot see the point. Their spreads are very wide.http://www.myfxbook.com/forex-broker-spreads
This is a spread comparison tool from myfxbook which compares live spreads. Not sure if the Alpari UK spreads are taken from their spreadbetting, but the GKFX certainly are.
GKFX is constantly amongst the tightest (despite being a SB) and always better than Alpari.
For entertainment value, watch the spreads on FXCM around news
I use an EA which trades AUDNZD. Alpari has a 12pip spread versus 6.5 usually with GKFX!
I monitor various brokers with this tool and, so far, GKFX and Hot Forex are constantly amongst the best.
(If this tool is accurate, of course)