Hi, I was wondering what the restrictions were on investing in companies.

Clearly, my ability to invest is dependent on what the brokerage company allows me to invest in. As far as I know, there are no restrictions on FTSE 250 companies.

However, when it comes to AIM listed companies, as far as I know, it's the arbitrary decision of the broker as to whether I can open up a position on any one specific company.

Also, are there restrictions on the types of positions opened; what I mean is will a brokerage allow me to buy shares in an AIM listed company but not allow me to place a spreadbet or open a CFD on the same company?