You could get away with probably 2k using high leverage however relative to the capital you could be wiped out in very little time. In other words you'll be employing excessive risk. If you are learning to trade you will be better off in demo. If you feel confident in your strategy you need to think of longevity with a business mindset. £5 a point and asking how much margin is needed isn't thinking with a business mindset. Realistically you need 10k to 20k to trade £5 a point with low risk.