At no point does the article actually say that plod found discs worth £1m. It says they found 30,000 discs and that they were found at a place "where pirate films, games and music – with an estimated street value of £1m – were produced." sic.

That £1m is more than likely an estimate of the street value of the forged goods that plod think were made at the facility since it was set up, or in recent weeks, or according to any indications of production qty they found at the place (blank disc containers etc) - i.e. they found 30,000 discs but reckon another 170,000 may have already gone out of the door: 200,000 x £5 = £1m.