Complex sentence: It was prompted by a technical shortcoming of petrol pump design: pumps (which were electro-mechanical) had been designed to be switchable between metric and imperial units, but had no provisions for prices above £1.999 per unit of fuel.
Split into simpler sentences: It was prompted by a technical shortcoming of petrol pump design. Although pumps (which were electro-mechanical) had been designed to be switchable between metric and imperial units, they were only designed to accept prices of up to £1.999 per unit of fuel.