Not sure why everyone thinks SB companies want you to lose.
They clean up so much on the spread, I'd imagine it doesn't really matter whether you win or lose.
Go direct market with say IB and sell a 10 lot in Crude (approx £75 per tick) and you pay market spread (1) and about £20 in commissions. So the trade costs you £20.
Do £75 per tick with a spreadbet company and you pay no commissions and 5 ticks above market (6) so the trade costs you 5 X £75 = £375.
So that's £355 over the top on every single trade you take in Crude.
The more unethical companies will try and screw you on the spread further by requoting and slippage.
VDM (now Gekko) is the only company I have had first hand experience of this with. They will shaft you silly.
At any rate, I don't think it's a bad business decision from Worldspreads.
They've cut all the markets to zero spreads that were 1 or 2 pips (with the exception of the Bund which is almost always 3).
So they lose 1 pip X stake per trade but probably get a huge amount of new client money. Undoubtebly most of the people that transfer to them are going to trade other markets at normal spreads too.
Ultimately, if you do a few trades (1 - 5) and make a decent return (e.g. 100 pips per week) its advantageous to SB.
If you are in and out all day long as most people on here seem to be, you are better off paying Tax.
There are a few minor considerations though. E.g. DMA often charge you exchange fees so if, like me, you trade markets as varied as USD/JPY one min and Carbon Emissions the next then you could rack up quite a few additional charges DMA.
Not to mention that the few hand holding elements like guaranteed stops that SB companies offer might save you in the long run if you are the kind of trader that likes to go long Lehmans on 100% margin. You don't get those in the Direct Market
Also, regarding the spread vs tax, remember you pay the spread each time but only pay your tax in a lump sum, meaning the money is in your hands for longer.