Can I withdraw my investment at any time?

If you are holding ordinary shares, there is no withdrawal.  The only way is to sell your shares to a willing buyer in accordance with the terms stated in the Shareholders’ Agreement or Limited Liability Partnership (LLP) Agreement.  

If its redeemable preference shares, the issuer of the campaign will state the timeline in which the shares will be redeemed (eg. 1 year from the date of funds raised) depending on the terms stated in the Shareholders’ or LLP Agreement.