Actually I don't think that's true Ethel
That's secion 1 and 2 of the act.
Section 3 reads:
3 Keeping dogs under proper control (1) If a dog is dangerously out of control in a public place�
(a) the owner; and
(b) if different, the person for the time being in charge of the dog,
is guilty of an offence, or, if the dog while so out of control injures any person, an aggravated offence, under this subsection.
http://www.opsi.gov.uk/ACTS/acts1991/ukpga_199 10065_en_1
And the 1997 ammendment reads:
4A Contingent destruction orders (1) Where�
(a) a person is convicted of an offence under section 1 above or an aggravated offence under section 3(1) or (3) above;
(b) the court does not order the destruction of the dog under section 4(1)(a) above; and
(c) in the case of an offence under section 1 above, the dog is subject to the prohibition in section 1(3) above,
the court shall order that, unless the dog is exempted from that prohibition within the requisite period, the dog shall be destroyed.
http://www.opsi.gov.uk/acts/acts1997/ukpga_199 70053_en_1