Apple's popular PowerBook G4 notebooks are in short supply, according to a number of UK resellers.

A report from O'Grady's PowerPage claims that the anticipated PowerBook upgrade has been delayed by engineering and processor supply problems. Motorola is reportedly supplying the chips for the new pro-notebooks. Some reports suggest any product refresh will be delayed until early August.

Apple's notebook line-up hasn't been upgraded since launch in January 2003, though the company did apply significant price reductions in June. This led many industry watchers to predict a PowerBook line refresh, if only to make Apple's lightweight aluminium alloy enclosure consistent across the range.

Despite feedback from Apple's UK reseller channel, the UK AppleStore today claims all PowerBook models are available for "same day" shipping. The US AppleStore says there is a five-day wait for most PowerBooks, excepting the 17-inch model.

Reports also suggest that demand for Apple's 17-inch PowerBook is falling off. Apple's usual response to slowing demand is to upgrade the product.

Apple does not comment on rumour or unannounced products.