A Ordinary Shareholders have pre-emption and voting rights (subject to the company's Articles of Association and the Companies Act 2006).
B Investment Shareholders (generally "the Crowd" given the price barrier to A shares) do not generally receive pre-emption rights, meaning there is a higher risk of dilution. Generally, B Investment shares also do not carry voting rights.
The different rights afforded by each share type typically reflect the amount invested by investors. The company raising funds can set the threshold of investment required in order to obtain A Ordinary shares.
Please read the Company's Articles of Association for full details of rights attached to your shares. These Articles are included in an email sent to investors before their investment is finalised. If you are not happy with rights in the Articles then you can query, reduce or cancel your investment before the expiry of the cooling off period, which will generally be no less than 4 days.