I know, how rude!
Was just noodling round HMRC web site and it said this
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What are the current rates of the national minimum wage?
There are three levels of minimum wage, and the rates from 1 October 2009 are:
* £5.80 per hour for workers aged 22 years and older
* a development rate of £4.83 per hour for workers aged 18-21 inclusive
* £3.57 per hour for all workers under the age of 18, who are no longer of compulsory school age
Development rate
The development rate for workers age 22 and over was abolished for pay reference periods starting on or after 1 October 2006. From that date, all workers aged 22 and over who qualify for the national minimum wage will be entitled to the main rate of national minimum wage. This applies even where the worker was previously in receipt of the development rate for those aged 22 and over and had been receiving that rate for less than six months.
from
http://www.hmrc.gov.uk/nmw/#b
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last bit may have confused the issue at certain places.
I reckon someone probably just forgot to update the computer. Hope you get it sorted