Margin trading means that you only deposit a fraction of the total value of any position that you open and you are therefore borrowing the remainder of the total consideration from the spread betting provider. In return, a spread betting provider will calculate the interest for that period and post it to your account each day that the position remains open. Therefore, each time that you hold a long position overnight, you may incur a small rolling charge. This charge reflects the fact that you are trading on margin.
Charges also exist on Daily Rolling Futures products and this is in respect of the administration required to maintain a position which would normally have a limited term, an expiry date, in this case one day. By offering you the chance to keep the position open for longer than the term, spread betting providers add a small daily charge to your account.