If at any time the number of members of a company is reduced, in the case of a private company, below two, or, in the case of any other company, below seven, and it carries on business for more than six months while the number is so reduced, every person who is a member of the company during the time that it so carries on business after those six months, and is cognisant of the fact that it is carrying on business with fewer than two members, or seven members, as the case may be, shall be severally liable for the payment of the whole debts of the company contracted during that time, and may be sued for the same, without joinder in the action of any other member.