It does seem crazy that the top of the unqualified scale is above the start of the main scale for qualified teachers. If it's in the state sector, the school has no choice but to pay you according to the school teachers' pay and conditions document, which clearly says: "42.1 An unqualified teacher who becomes qualified shall transfer to the next point on the pay scale above the sum of his salary, or to such higher point as the relevant body consider appropriate."
Look at the information at www.teachernet.gov.ukmanagementpayandperformancepay. Within each pay scale there are four separate bands (London weighting is no more) depending on whether you work in inner, outer or the fringe of London, or elsewhere in England and Wales. If you're outside London, you'll be getting pound;22,023 as someone on point 10 of the unqualified scale. Since you have to be transferred to the main scale for qualified teachers and not lose out financially, you are entitled to be put on M3, pound;22,338. This goes up in September 2006 to pound;22,899.
If you think you are worth more because of relevant experience, state your case clearly in writing to the chair of governors.