Brokers must adhere to ESMA regulations which dictate the maximum margin (or leverage) they can offer to clients. The margin available varies according to the instrument you want to trade, but is restricted to:
5:1 leverage on equities & bonds (20% margin)
10:1 leverage on commodities (10% margin)
20:1 leverage on major indices & gold (5% margin)
30:1 leverage on major currency pairs (3.33% margin)
If you need more leverage, many brokers off professional accounts with higher margin levels. However, these accounts have a strict vetting process and you must meet certain requirements in order to open one.