You can leave it in your paypal account for as long as you want...you won't get charged for that. All it means, is that next time you pay via paypal, the money will be taken from your account, rather than your bank account. It also means that the person recieving the money wouldn't have a fee deducted when they get it

Either that, or just wait till you recieve more money and then when your paypal balance is £50 or above, you wouldn't get charged for transfering it to your bank account.