Apple has raised its stake in Imagination Technologies, a British designer of microchips used in laptops and smartphones, marking the latest escalation in a recent buying spree for shares in the Hertfordshire-based group.

The increased stake takes Apple’s holding to 9.5 per cent and follows a surge in trading in recent weeks that saw exchange volumes for the group’s stock surge 90-fold as Apple and Intel snapped up shares. Shares in Imagination have risen by 60 per cent since the start of June and have trebled since December.