An underwriter at a Lloyd's may limit his total liability on all risks to the amount of his subscription as expressed in his power of attorney and agreement with the attorney-in-fact; provided at least half of the subscription of each underwriter must be paid or contributed to the guaranty fund in cash or admissible securities. Each underwriter shall be responsible solely for his own liability as fixed in the contract of insurance and shall not be liable as a partner and in no event shall the liability of an underwriter exceed the amount of his total underwriters agreement executed in favor of his respective successor attorney or attorneys-in-fact.