I beleive that if you want a credit account, the SB company would look for evidence that you have liquid funds elsewhere of significant value which could be called upon in the event of a margin call and could be transferred immediately.
If you don't have any other significant liquid funds, I doubt you would get a credit account.
The reason a "notional trading requirement" is required is that most stops are not guaranteed and a position could go beyond your stop, thus requiring more margin.
In the above example with CMC, a notional trading requirement (NTR) with CMC of 100 on the dow means that if you open a position of £1 per point. You will require £100 to maintain that position. However, if the position goes 70 points against you, you still have a 100 point NTR and you would have to stump up another £70 to maintain the position.
I am not sure what the minimum account size is with CMC but if you opened an account with £500, you would have a bank that would allow a few trades on the daily dow without being shut down if one trade goes against you. Beware though, even with £1 per point, it won't take many bad trades to wipe you out.
Another idea may be to look at IG. I'm not sure if they still do this but they used to allow you to open an account with no initial deposit. You could only ever place trades with a guaranteed stop (which of course makes the spread wider) but that then allowed you to fund each trade at a time, depositing the amount required to cover the guaranteed stop by debit card. ie if you have a 50 point stop at £1 pp, you paid them £50). This is what I did at first, but it was about 3 years ago now.
Hope this is of help
