Margin trading involves the use of leveraged position sizes where relatively small amounts of money can be used to fund much larger positions. For example, a trade using 10:1 leverage would enable a trader with £10 to open a position size valued at £100. In this case, the extra £90 is borrowed from the spread betting provider to enable the trader to maximise potential gains (or losses, if the position does not work as anticipated).
Providers typically make margin requirements forcing traders to have a certain amount of money available in the trading account (generally anywhere from 0.5% to 10% of the total trade size) to keep the margin trade open and active. You should remember that, while margin trading can allow traders to maximise gains through larger position sizes, losses can be equally enhanced and you will be responsible for these losses if the trade moves adversely.