The MOD system is set up with a payspine and target rate. CS's move up one point on the payspine each financial year (always assuming the unions/MOD agree payrise in time), until they hit the 'target' salary rate for the grade.
On paper and in theory an EO could just about earn 30k, BUT it would only be the most senior members of the grade who got it. On average the unions reckoned it would take 20years for most grades to hit their target salaries.