There
is no "underlying transaction", Charlie.
That's the whole point: you're
not buying or selling anything, when you put on a spreadbet - you're simply having a "pounds per pip" bet on a price-movement. That's why spreadbets are defined in units of "pounds per pip", and
not in terms of lots/minilots, or whatever.
And it's why you can't compare different spreadbet companies according to their "available leverage" (
which was what the OP asked!).
If you choose to open a spreadbet position for $10-per-pip (or its GBP equivalent) on the EUR/USD, your position will be equivalent to buying "one lot", but there's
no leverage,
per se, involved.
Being aware that you and I have both been trading at Cap-Spreads for rather a long time, I'm rather surprised to see what you've said, on this subject, and respectfully I think you're missing the point of the OP's question. He's thinking of it (inappropriately) in leverage terms and wants to know how he can effectively get the most per pip for his stake-unit. His answer is that
it makes no difference: he'll get the same mileage everywhere for his "£1 per pip" or "£5 per pip" or £100 per pip" or whatever he wants to stake, because there's no underlying transaction and
no leverage. Not only is this simply factual, but
it's also what he needs to know, to answer his question: it makes no difference which spreadbet company he uses, if that's his objective.