thanks BeeBop
Interactive Brokers (IB) definitely look a lot cheaper.

re: service levels. Yesterday I asked the same question of both Internaxx and IB. It was a genuine question - whether they allowed trading of all AIM shares. I have some niche little holdings and I'd like to be able to add / sell them when I move brokers.
I got a very fast response from Internaxx - yes. I also emailed a third player - Hargreaves Lansdown - who replied within a couple of hours. But 24 hours later, I'm still waiting for IB to reply.

So I think my decision is coming down (perhaps unsurprisingly) to better service vs lower prices. I must be a tight-arse as I'm leaning toward IB (assuming they can trade all AIM).